Just to poke my 2 cents in, it might be something as simple as adding another sub animation to an existing one with a slight alteration in the positioning as well as specified modifier into a girls xml. With that I thnik you'd have to also add it into the extra sexual positions pack for it to work, you know how theres various things that can be where you'll click an icon on the screen and it will add a hand or go to a variation of like say against the wall, It would probably have to be done that way.If that might help get an idea how it "could" be done.Like I said it's just my 2 cents and I'm not sure on all the specifics of your process. For all I know your way to getting it figured out.
Hope that helps or gives you an idea,
-Temp