Does anyone have any ideas about how to "tuck" a dynamic shirt inside pants?

I've been experimenting with this, and the best idea I've come up with is to add a torus prop, move it to the waistline of the pants, add it as a collision object for the shirt, and gradually shrink it over the course of the simulation.  It works, but I'm wondering if there's a way to do this that's a little less--what's the word?--dorky.

Thanks