How should a disciple of the Buddha with great samadhi verify that rebirth occurs after physical death? I asked my teacher how somebody should see for themselves that rebirth occurs, he (a Theravadin monastic) said that with great samadhi one should watch the twelve nidanas (the process of dependant co-arising) to see the eleventh nidana (becoming leads to birth).

I can accept that if one watches the nidanas then one would see that becoming leads to birth. However, seeing birth occurring during our (biological) life is separate from concluding that (re)birth occurs after physical death. I think that the most simple way to put this is that the process of becoming leading to birth is not dependent on the body. If one can see the eleventh nidana then how would they confirm that the eleventh nidana does not require form?

Perhaps I am on the wrong track entirely and the proper action is to watch some other process to see that the mind (instead of just the nidanas) does not require a body to sustain it.
Yes. This question is on the wrong track because Dependent Origination is only about the 12 conditions that result in suffering, i.e., sorrow, lamentation, pain, grief &amp; despair. To quote:


  And what is dependent co-arising? From ignorance as a requisite condition come fabricators. From fabricators as a requisite
  condition comes consciousness. From consciousness as a requisite
  condition comes mentality-&amp;-materiality. From mentality-&amp;-materiality as a requisite condition
  come the six sense media. From the six sense media as a requisite
  condition comes contact. From contact as a requisite condition comes
  feeling. From feeling as a requisite condition comes craving. From
  craving as a requisite condition comes clinging. From
  clinging as a requisite condition comes becoming. From
  becoming as a requisite condition comes birth. From birth as a
  requisite condition, then aging &amp; death, sorrow, lamentation, pain,
  distress &amp; despair come into play. Such is the origination of this
  entire mass of stress &amp; suffering.
  
  Paticca-samuppada-vibhanga Sutta: Analysis of Dependent Co-arising


In other words, the 12th nidana is not about physical death. The following quote states aging-&amp;-death cease when 'the eye sees a form', i.e., while the physical body is still alive: 


  On seeing a form with the eye, he isn't infatuated with pleasing
  forms, and doesn't get upset over unpleasing forms. He dwells with
  body-mindfulness established, with unlimited awareness. He
  discerns, as it has come to be, the awareness-release &amp;
  discernment-release where those evil, unskillful qualities cease
  without remainder. Having thus abandoned compliance &amp; opposition, he
  doesn't relish any feeling he feels — pleasure, pain,
  neither-pleasure-nor-pain — doesn't welcome it, doesn't remain
  fastened to it. As he doesn't relish that feeling, doesn't welcome it,
  &amp; doesn't remain fastened to it, delight doesn't arise. From the
  cessation of his delight comes the cessation of clinging.
  From the cessation of clinging comes the cessation of
  becoming. From the cessation of becoming comes the cessation of birth.
  From the cessation of birth, then aging-&amp;-death, sorrow, lamentation,
  pain, distress, &amp; despair all cease. Such is the cessation of this
  entire mass of stress &amp; suffering.
  
  MN 38


When someone or something you love &amp; are attached to dies, you suffer. This is because the mind previously took 'birth' ('jati') via becoming ('bhava') as a 'self-identity' ('sakkhaya') attached ('upadana') to the sense object ('ayatana') that passes away ('marana'). 

For example, you identify yourself with a sense object that is a woman that you call 'my wife' &amp; you call yourself 'her husband'. If your wife physically dies (by physical death) or the legal status (convention) of 'wife' socially dies (by divorcing you), your self-identity as a 'husband' also 'dies', which is suffering. 

Or when you look into a mirror &amp; see your skin wrinkling, your hair becoming grey, your teeth rotting, etc, you suffer due to the thought: "I am aging, I am going to die". These thoughts produce suffering because those five aggregates that appear in the mirror the mind regards to be "I", "me", "mine" &amp; "myself". 

For example, you may watch TV and see 10,000 Chinese people die in an earthquake but suffer more if you see your pet dog, pet cat or pet goldfish die. You may suffer more if your favourite pen is stolen. This is because the mind identifies with &amp; is attached to the pet dog, pet cat, pet goldfish or pen but not attached to the 10,000 Chinese people. The death of 10,000 unknown Chinese people do not cause suffering but the death of a pet cat causes tremendous suffering. 

Aging-&amp;-death in Dependent Origination refers to the aging-&amp;-death of 'beings' ('satta') and the various orders of 'beings'. 'Beings' ('satta') is defined in the suttas as states of attachment &amp; identity (rather than physical life forms). 'Satta' is merely a 'view'. 

The relationship between the nidanas of birth (self-identifying) &amp; aging-&amp;-death (suffering due to loss) is explained simply below: 


  He assumes consciousness to be the self, or the self as possessing
  consciousness, or consciousness as in the self, or the self as in
  consciousness. He is seized with the idea that 'I am consciousness' or
  'Consciousness is mine.' As he is seized with these ideas, his
  consciousness changes &amp; alters, and he falls into sorrow, lamentation,
  pain, distress, &amp; despair over its change &amp; alteration.
  
  Nakulapita Sutta


You may ask yourself when suffering: "Why am I suffering?". The general answer is because of change &amp; loss, i.e., aging-&amp;-death. Then ask: "Why did aging-&amp;-death cause me to suffering?" The answer is because I ignorantly regarded the lost or deceased object to be "I", "me" &amp; "mine"; I took birth as the 'owner' of those objects. 

Below is what famous Thai monk Ajahn Chah had to say about this:


  Now, how do we know that it's a bhava? It's a bhava (sphere of existence) because of our clinging to the idea that those trees are
  our own, that that orchard is our own. If someone were to take an ax
  and cut one of the trees down, the owner over there in the house
  ''dies'' along with the tree. He gets furious, and has to go and set
  things right, to fight and maybe even kill over it. That quarreling is
  the ''birth.'' The ''sphere of birth'' is the orchard of trees that we
  cling to as our own. We are ''born'' right at the point where we
  consider them to be our own, born from that bhava. Even if we had a
  thousand apple trees, if someone were to cut down just one it'd be
  like cutting the owner down.
  
  http://www.ajahnchah.org/book/Flood_Sensuality1.php


This taking 'birth' as the 'owner' of sense objects is explained in the definition of 'birth', below: 


  And what is birth? Whatever birth, taking birth, entering, coming-to-be, coming-forth, production of the the various beings in this or that group of beings via the manifestation (distorted perceptual appearance) of the five aggregates &amp; acquisition (taking ownership) of sense media (objects), that is called birth.
  
  Paticca-samuppada-vibhanga Sutta: Analysis of Dependent Co-arising


Again, the same Pali term for 'acquisition' is used below:


  yāyaṃ attabhāvapaṭilābho yasmiṃ attabhāvapaṭilābhe attasañcetanā
  kamati no parasañcetanā, attasañcetanāhetu tesaṃ sattānaṃ tamhā kāyā
  cuti hoti
  
  ...in that acquisition (paṭilābho) of individuality (attabhāva;
  self-becoming) in which one's own volition (attasañcetanā) operates
  but not the volition of others (parasañcetanā), it is by reason of
  their own volition that beings (sattānaṃ) pass away (cuti; shift;
  vanish) from that group (kāyā)
  
  AN 4.171


The sutta below states whenever objects of consciousness are appropriated or 'stolen' to be "I", "me" &amp; "mine", there will be inevitable punishment or suffering. 


  "And how, O monks, should the nutriment consciousness be considered?
  Suppose, O monks, people have seized a criminal, a robber, and brought
  him before the king saying: 'This is a criminal, a robber, O Majesty!
  Mete out to him the punishment you think fit!' Then the king would
  tell them: 'Go, and in the morning strike this man with a hundred
  spears!' And they strike him in the morning with a hundred spears. At
  noon the king would ask his men: 'How is that man?' — 'He is still
  alive, Your Majesty.' — 'Then go and strike him again at noontime with
  a hundred spears!' So they did, and in the evening the king asks them
  again: 'How is that man?' — 'He is still alive.' — 'Then go and in the
  evening strike him again with a hundred spears!' And so they did.
  
  "What do you think, O monks? Will that man, struck with three hundred
  spears during a day, suffer pain and torment owing to that?"
  
  "Even if he were to be struck only by a single spear, he would suffer
  pain and torment owing to that. How much more if he is being struck by
  three hundred spears!"
  
  "In that manner, I say, O monks, should the nutriment consciousness be
  considered. If the nutriment consciousness is comprehended,
  mind-and-matter are thereby comprehended. And if mind and body are
  comprehended, there is, I say, no further work left to do for the
  noble disciple."
  
  Puttamansa Sutta: A Son's Flesh