Stained Glass /Mosaic-like filter

I'm looking for a process that will yield results similar to the Stained Glass Filter in Photoshop but allows user to define the shape of the cells. If you are not familiar with the effect, basically I need to be able break up a plane into shapes that average the colors behind(/inside) them. I think this might require opengl trickery and I am an artist, not at all a programmer. Any help would be appreciated.

Thanks,

C