But what if he's not a pugilistic kinda guy? He might also not be thrilled wih the idea of being up on assault charges.
KIS's idea is interesting:
One point of leverage, the recording they're using is of your performance. You can tell him that he's using your performance without your permission (as he's not honoured your verbal agreement) and you want it withdrawn. That'll leave him with the cost and hassle of a new drum recording.
Trouble is, it might be hard to let go of a milestone like the first performance on an album. But if you're uncredited you'll be in the situation where no one but friends will believe you. But how to prove it's your performance and not the other drummer's?
A bit surprised that the other drummer is going along with it. How can he be happy with being credited for another drummer's performance?