Enter any of these passwords at the password screen:

Sweet Tooth: start, R1, right, right, left
Crusher: down, R1, right, R1, L1
Moon Buggy: start, triangle, right, L1, start
RC Car: up, down, left, start, right
Super Auger: left, circle, triangle, right, triangle
Super Axel: up, right, down, up, L1
Minion: triangle, L1, L1, left, up
Super Thumper: circle, triangle, start, circle, left
Super Slamm: right, L1, start, circle, start

You should now have the vehicles that you entered at the password screen!