there is something called a "waspinator"
http://www.amazon.com/Unknown-WASP1-.../dp/B002ITNBT8
i have no idea if it works, but worth a shot for under 10 bucks. i also remember a sewing pattern to make one. but can't remember where i saw it. google it as a pattern and see if you come up with something.
i try to keep up with the ones i see..in the evening i spray where the nests start..(in my grill is a constant fight)