An air dam extension might work. The car is currently shaped to push a bunch of air under, so an air dam that's even with the front of the bumper could help keep air from going under the car so much.
OTOH, a belly pan might make that point moot.
Edit: Posted that while Jay was writing the above post. Jay, I didn't know about your air dam extension working out the way it did, did you post about removing it? I thought it was commonly accepted that somewhat of a vacuum under the car is a good thing because the underside is so non-smooth.
Perhaps wheel deflectors/wheel air dams?
You may be able to point the nose a little bit. One of our members with a Cavalier did so.
He's also got rear and partial front fender skirts, wheelcovers, and what looks like side skirts (or whatever they would be called).
For some extreme aero mods, see basjoos AeroCivic: