Have you ever wonder how those killer magazine covers are shot with the car in focus and everything else behind in motion..
<-- This is what you need.
Hardware attaches to the bottom of the car on one end and the other to your camera. Then set your camera to the desired shuttle speed and aperture. Next have the owner sit in the car and pretend to drive and have another person behind the car slowly push the car. That, my friend is how those Photographers make hella $$$, all thanks to a few metal braces that latches itself to you car.
Check out the attached photos for inspiration. If you are interested in this product, go check out: Automotive Rigs