Sweet Tooth:
Enter Start, R1, Right, Right, Left as a password at the options menu.

Crusher:
Enter Down, R1, Right, R1, L1 as a password at the options menu.

Moon Buggy:
Enter Start, Triangle, Right, L1, Start as a password at the options menu.

RC Car:
Enter Up, Down, Left, Start, Right as a password at the options menu.

Super Auger:
Enter Left, Circle, Triangle, Right, Down as a password at the options menu.

Super Axel:
Enter Up, Right, Down, Up, L1 as a password at the options menu.

Minion:
Enter Triangle, L1, L1, Left, Up as a password at the options menu.

Super Thumper:
Enter Circle, Triangle, Start, Circle, Left as a password at the options menu.

Super Slamm:
Enter Right, L1, Start, Circle, Start as a password at the options menu.

For all these codes, the sound
of laughter will confirm correct code entry.
These are all untested codes, but they're from APi's cheats section. *Good luck.