In reality, there is very little "forced" anything in professional sessions. It's usually all a mental game or negotiated role play.

In situations where I have known the sub well and decided to expand his limits by including something like feminization, I have employed a variety of tactics from bondage (he's completely tied up and I start applying makeup as an example) to simply demanding he put on the clothes I am offering him.

I have had subs protest but I have never had one completely refuse. Of course, forced fem is completely different from forced bi or forced toilet - both of which have potential health impacts in addition to the psychological.