Here is how you walk around a stunt track.(READ IT ALL)
1. Have two players go in a stunt track.
2. Have one player start their own race by themselves.
3. while the lights blink for the countdown of the race, the character that is not in the race run the other over.(Do it before the last green light ends)
4. Now the player that was run over can walk without a car! They can now use items like the camera or the weapons.
5. If the other player wants to do that, let them start a race, and the character walking shoulder charge the person who is about to race.
***PLEASES NOTE THAT GOO MAY NOW NOT BE EJECTED OUT OF THE CAR. IF YOU WANT TO UNDO GOO, USE THE OPPOSITE GOO.***Also you can get in and out of the car easily. If you want to leave the stunt track, get back on the car and exit normally.
**Also try to avoid spots you can get stuck in without a car.***
This may or may not work for other platforms like the PS3 or PC you can try it though.