Not sure of the specifics, and it would probably be a chore, but you could edit the animation package files so the "clothes based on pose" setting lines up more with what you'd like. However, as far as I know there's no way to dynamically change clothes during sex. This mod is pretty buggy around outfits in general, it's quite easy to get a sim into a loop of trying and failing to get dressed, for example.
Guessing you've seen this, but characters can take off top/bottom via Kinky->Exhibition->Undress [Top/Bottom] and the results will carry over into the scene, but these commands can't be used during Woohoo.