If you were dealing with HMRC (UK) rather than IRS (USA) then no matter where you are based I would strongly recommend that you contact them directly and ask them for their advice. As a director of two companies I have found that they are helpful beyond expectations. The people I deal with are there to ensure that everything is legal and above board, they are not there to make you pay as much as possible. More than once I've had HMRC make suggestions that would reduce what I pay, and their advice is free.
Sadly, youa re dealing with the IRS, and I have no idea if they are the same. The impression one gets from outside the USA is that you must pay professionals for their advice and assistance in dealing with Government agencies, rather than dealing with the agencies themselves.
IANAL, and in particular I have no direct experience f taxation issues in the USA, but my advice would be to find an accountant in the USA who is willing to discuss this will you via email. Your friend should be able to find one, and I suggest he might be legally required to do so. In return, you should sort out some way for him to get compensation, because most likely it is he taking the risks on your behalf.