I think you would opening up yourself for all kinds of problems with the FAA. They will see through the thinly veiled disguise of "shared expenses" and "I'm only charging for my time."
You might get away with it for a little while if by "share expenses" you mean half the fuel right? right? And you're only charging $20-$40 per hour (give or take).
If you start charging $150/hr for your "time", you will be in trouble. If you set this up as a business, there is no veil at all.
It's really doesn't matter what you are doing, it the perception of the FAA that counts, and the FAA says commercial ops and renting an experimental aircraft are a no-no.
However...There is the option for getting a "LODA", letter of deviation authorization (or something like that) that will allow you to charge for your time and expenses for the purposes of transition training (usually required by insurance companies). From what I understand these are very difficult to obtain and many FAA people are clueless as to what it is and how to get one. But it is possible. Getting one to provide acro instruction will most likely never happen.
(I'm building an RV7 have done a fair amount of research on the subject. Disclaimer: everything I type can be and probably is wrong. )