Point them down through holes in the floorboards to levitate the car a little bit. Lessens weight, improves gas mileage.
Assuming his vehicle is rear-wheel drive, there's a threshold issue with this. Below a power/displacement threshold (depending on the weight of his vehicle) all he'll do is reduce traction to the wheels providing power to the vehicle. Very dangerous. Above the threshold we enter into hovercraft territory.
The obvious solution here is tons of displacement and power. Not to mention formatting all of your music for gapless playback. Your hovercraft won't function with a 2-second gap between tracks
