I came up with this when a "built in" belt on a pair of outdoor pants I have was cut. I like this "temporary" belt so much my field-expedient replacement still resides on those pants! However, in this video I use a loop and two strand diamond knot; on mine I use a loop with monkey's fist knot instead.

http://www.youtube.com/watch?v=tQ9VL2IVlFM