Yep, I know what you mean about the hand cramps... my boyfriend's gone through the exact same process at times to get me off. I felt really bad afterwards (and during) as I was aware it wasn't comfortable for him.

Still, the thing that comforts me somewhat about it is that sometimes I get jaw pain from giving him blowjobs for extended periods of time. (He doesn't want to perform oral sex on me in return but that's a WHOLE other story...)