How do Bodhisattva vow takers avoid stream entry? According to the suttas in SN13, a stream enterer (or stream winner or sotapanna) only has at most, seven remaining lifetimes, before they are permanently freed from suffering.

On the other hand, takers of the Mahayana Bodhisattva vow, would forego enlightenment for a very long time (apparently aeons), till they complete the full Bodhisattva training (which I presume is the development of paramitas and the attainment of bhumis).

However, this implies that they need to avoid stream entry, which could cause them to become released from suffering in seven lifetimes at most.

So, how do they avoid stream entry? Do they avoid it by avoiding the practice of insight meditation (vipassana) perhaps?
I think that Mahayana literature teaches that becoming an Arhat is a temporary rest, for example:


  Mahayanins are urged to instead take up the path of the bodhisattva and to not fall back to the level of arhats and śrāvakas. Therefore, it is taught that an arhat must go on to become a bodhisattva eventually. If they fail to do so in the lifetime in which they reach the attainment, they will fall into a deep samādhi of emptiness, thence to be roused and taught the bodhisattva path, presumably when ready. According to the Lotus Sutra, any true arhat will eventually accept the Mahāyāna path.


Or from The Jewel Ornament Of Liberation by Gampopa,


  III. HEARER FAMILY
  
  The family of Hearers consists of those who fear samsara and yearn to achieve nirvana, but who have little compassion. It has been said:
  
  
    One who is afraid upon seeing the suffering of samsara
    And yearns to achieve nirvana
    But has little interest in benefitting sentient beings—
    These three are the marks of the Hearer family
  
  
  IV. SOLITARY REALIZER FAMILY
  
  The Solitary Realizer family includes those who possess the above three attributes and in addition are arrogant, keep their masters’ identities secret, and prefer to stay in solitary places. It has been said:
  
  
    Fear at the thought of samsara, yearning for nirvana,
    Little compassion, arrogance,
    Secretive about their teachers, and enjoying solitude—
    A wise one should understand that these are the marks of the Solitary Realizer family
  
  
  So these two families, the Hearers and the Solitary Realizers, engage in their respective vehicles and even though they achieve the results of their practices, these results are not the final nirvana. How do they abide when they achieve their fruits? They maintain unafflicted states of meditative concentration, but those states are based on the psychic imprint of ignorance. Since their meditative concentrations are unafflicted, they believe that they have achieved nirvana and remain that way.
  
  If their states are not the final nirvana, then one might argue that the Buddha should not have taught these two paths. Is there a reason the Buddha should teach such paths? Yes. For example, suppose great merchants from this Jambudvipa are traveling the ocean searching for jewels. After many months at sea, in some desolate place, they become completely tired and exhausted and think, “There is no way to get the jewels now”. When they feel discouraged and prepare to turn back, the merchant captain manifests a huge island through his miracle power and lets all his followers rest there. After a few days, when they are fully rested and relaxed, the captain says, “We have not achieved our goal. Now we should go farther to get our jewels.”
  
  Similarly, sentient beings without courage are frightened when they hear about the Buddha’s wisdom. They believe attaining Buddhahood is a great hardship, and think, “I have no ability to do this.” There are other people who are not interested in entering the path, or who enter the path but turn back. To counter these problems, Buddha presented these two paths, and allows them to rest in these states.
  
  As said in the White Lotus of Sublime Dharma Sutra:
  
  Likewise, all the Hearers
  Think that they achieved nirvana,
  But they have not achieved the final nirvana
  Revealed by the Buddha
  They are only resting
  
  When these Hearers and Solitary Realizers are well rested in those states, Buddha understands this and encourages them to attain Buddhahood. How does Buddha encourage them? He awakens them through his body, speech, and wisdom mind.


Also this question has been asked on other sites, for example on reddit and on 
Dharma Wheel.