To make it easy.
Make the body part you want to replace invis, either in the scene tab, or of it´s not possible there, by changing the opacity in the advanced surface tab to 0.
THen put the other figure over the first, make anything, you don´t want invis, et voila.
Adjust.
There you go. ;)

On a side note, changing the opacity might bringt different results, than making it invis in the scene tab.

Just try it out.