Mode to Cheat
Go to the screen which says: "Press Start", hold L2 + L3 + R1 + Down + Square + Circle. Do this in this order or else it will not work properly. All skiers including Skier X, costumes, and ski units will be unlocked.
Bonus characters
Complete all the tracks and win a gold on the San Francisco race to unlock Phat Earl, Miki, and Skier X.