I would use the IEP for sure. I wouldn't consider it "using the disability card" even though other kids in the class are affected and won't necessarily be helped by doing it that way.
I am selfish when it comes to my kid because I don't have the time and energy to help all the kids. I am my kid's advocate; other parents are their kids' advocates.
Also, probably pulling out the IEP is the only way you can be sure to get results. A general letter of complaint will be ignored if this teacher is doing this to the whole class. For whatever reason, the school is holding on to this teacher and there is no way other parents haven't complained.
Use the ammunition that you have, the IEP, and do it!
(Likely, you will be helping the other kids because this teacher isn't going to give a project to just your kid...it is easier to give them all the same thing.)
Ugh! Good luck! Nan