I think the only way you can do it is if you send the car to someone who has made the logos you're after, have them apply them and then they send it back. I maybe wrong but I think thats what I read somewhere for Forza 3.
Failing that, have some patience and recreate the logos yourself.
Keeping the camera in the same place, take two screenshots. One with the car and one without. Place the two images one on top of the other (one with the car on top) and then cut the car out. Apply motion blur to the bottom layer and you shouldn't get the blurred edges on the car.