Inflate Deformer

I was discussing with a colleague recently on how to create a deformer that simulates a foot stepping into snow.

I decided to give it a go myself and the results aren't too bad. Most of the work was already done with the collision deformer I put together previously, the most difficult part was getting the mesh to inflate back to it's default shape. There's a great demo by Marco D'Ambros on this sort of effect.