Under the easy difficulty setting, choose Maui. Towards the end of the race (snowboarding), go to the left on the last grind rail.
Expert difficulty setting
Win first place under the hard difficulty setting.
Hard difficulty setting
Win first place under the easy difficulty setting.
Hidden course
Select the Himalaya track under the easy difficulty setting. Enter the "skeleton" tunnel, and turn to follow the alternate route to the left. Collect the medallion to unlock a hidden ATV course.
Bonus trick medallion...