Can (part of) the fuel in your tanks be considered "property carried for compensation or hire"? This question brings up that an experimental category aircraft cannot carry "persons or property for compensation or hire".  However, this raises a question regarding civil-registry refueling tankers (such as the venerable N707MQ).

Since the tanker is carrying fuel on behalf of another entity (the military unit they're contracted by to pass gas to) for compensation (contract payments), wouldn't the fuel that has been offloaded on-station be considered "property", backing N707MQ and its experimental (market survey) airworthiness certificate into a proverbial corner?

(Yes -- I know that contract tankers are considered Public Use aircraft when on-mission, which probably renders 91.319 moot, but it could easily be the case that a contract could say "operate IAW FARs with the exception of refueling operations", which'd inadvertently loop 91.319 back into the situtation.)
N707MQ actually has a special type of experimental certificate, according to its registration it is a "Market Survey" aircraft as you note.

The FAA defines this as 


  Market surveys:  to conduct market surveys, sales demonstrations, and
  customer crew training for U.S. manufacturers of aircraft or engines.


This does not really provide us any special way to use the aircraft for commercial purpose but is worth noting. 

Either way as you state 91.319 pretty clearly prohibits this. Interestingly enough 91.905 even prevents you from getting an FAA waiver to override 91.319 (as its not on the list of things you can have waved).

However 91.319 sub section H may provide us with a solution. 


  (h) The FAA may issue deviation authority providing relief from the
  provisions of paragraph (a) of this section for the purpose of
  conducting flight training. The FAA will issue this deviation
  authority as a letter of deviation authority.


As far as I know these tankers are primarily used in our own airspace for training missions which would fall under "conducting flight training".

This article is pretty interesting and covers a similar scenario for using experimental for commercial purposes.