Just gave it a shot. It doesn't quite fit, the handle is a bit too big at the base to fit in Classic Prime's fist-holes. Since the gun is rubbery, you might be able to squish it and wedge it in... or just carve about a half-millimeter off the corner of it, and it would probably work. But it doesn't quite fit right out of the box, sorry!
Sorry to bring this back up, but if I were to somehow fit it, how's the size? Is the gun a good size for classics prime? Anyone have pictures (you don't even have to force the gun to fit if you don't want to. Prime next to the gun would be fine)?