[lunarhighway]

adjustable airdams have been thought of, but i think you're better of in the real world with something that can stand up to the abuse.
the gm volt seems to go that route too.

you might want to look at linoleum, vinyl or a similar flooring material, places that sell and place the stuff might have undesized leftovers you can have or they sell for very little don't look at the color, a shot of black spray paint will render it invisible... something that's undersized as a flooring marterial can still be several square meters, and it's pretty strong. some types are brittle but others will flex so hitting something won't be a problem and at worst it'll grind away where it hits.. i'd secure it with self tapping wood screws into the back or the bottom of the plastic bumper leaves a tiny hole that noone will ever see in case you end up.

considdering the potential savings you can spend a few dollars on decent material and have the mod pay for itself over a relative short time