You're thinking of the liquify tool. The original version of WM had a couple girls made prego this way.
With dedication and time it's quite possible to make it work pretty well. However, I doubt anyone can make it as good as the original image. Here's a quick example of my own:
Before:
After:
The true task is to find a suitable image that will work for it. This was done super quick but you can see the issues with it. The lighting and shading is all kinds of messed up. At the current size of the images in-game it won't be as noticeable though. Unfortunately when we get a full screen mode it'll be quite the opposite.
(I should of used a hard eraser. :x)
Sorry for the huge images... at least you can use it if you want? lol
