You can take a gamble and wash them in hot water, but then you can't really control how tight they get. If you have some time to invest in it, put them on and get in a bathtub filled with hot watter. When they get around where you want them, get out.
I think The Gap actually sells jeans with instructions on how do to just that, kind of a way to get custom fit jeans for a reasonable price.
The only problem though...after you've had them on for a few hours, they seem to go back to the previous fit anyways.
I'm trying to decide if its worth washing them in hot water and seeing what happens. I actually have two pairs I could shrink a little. Maybe I'll just do one at a time, if the first works, I'll try the second pair.