Go to the options screen then press C-Down +R, C-Left + R or C-Up +R. You will see at the bottom a window which has popped up that lets you modify a 16-bit register. You are only allowed to change the first 6 bits. To do this you must hold :

C-DOWN +R = CHANGES HEAD SIZE
C-LEFT +R = CHANGES BODY SIZE
C-UP +R = CHANGES HEIGHT

CODE                    WHAT IT DOES

010001                  elongated players, large heads, large announcer
010101                  large players, large heads, large announcer
010010                  crunched players, large heads, small announcer
110110                  large players, small heads, large announcer
000001                  elongated players, large announcer
000010                  crunched players, small announcer
000100                  large players, large announcer
001000                  small players, small announcer
110000                  stocky players, small heads
010000                  stocky players, big heads
100000                  stocky players

Go to Olympic mode and select Freestyle Aerials. Then pick any trick. As you go down the hill don't press any button. Wait until you have left the ramp then rapidly tap the B button. When you land your skier will jump forward and land on his head and continue to ski down the hill with his head in the snow.