Not much time for me to delve into the net tonight, but here's just a little transformative sketch I found. Hidden cocks emerging from tight orifices is right up my alley.

http://www.furaffinity.net/view/21928158/

It reminds me of futakitty's fk_Vagina photomanips (http://www.f3.to/f3/galleries/futa-kitty/PhotoManips/)
, except of course, this is a step toward the animalistic side. It could also be seen as a female to male TF, if that's your thing.