turning a mesh file inside out?

[gaittec]

I need to know if there is a way to turn a 3d stl mesh file inside out.

Here's my project. Think of a footprint in sand. Scan the foot print. This gives you a negative (reverse) copy of the surface of the foot. Now I need to turn that negative scan inside out so that it is a positive copy of the foot.

I hope this is clear. I will actually be scanning foam impressions of feet and than I want to reverse them inside out so I get a mesh file in stl that is as if I had scanned the actual foot directly.