How about this? This was something I put together a while ago. You have also the option of car rigs. They get expensive but they work.
Heres how I had to work. A rig was mounted and then a capture taken when stationary to use the lines for the final picture. Since there is no motion, the learning lines such as joints for body panels are at their sharpest. Not one foot of the rig is removed also.
Setup
The car is then set into motion for the rest of the capture.
Shot
Then I have to go crazy and spend time in PS finalising the shot. Had to use a stupidly small app due to no available ND grad. Was ISO50 @ f/22 and still only managed 1/3 second.
The final shot
[Larger Version]