Falling crate

[grover]

I'm trying to make a pushable crate that falls off when it gets to the edge.
So far, I've got a poly that I can push, and a platform textured the same as the poly that lowers when I get to the edge. It gives a pretty decent illusion of the crate falling. My problem is that the poly remains in the way once the platform goes down.
Is there a way to remove a poly that I no longer need?

[neoworm]

What about using pushable 3D model? Something like this was made in Portal.