what i do to unlock them all is go to alaska, put a starting point at the top of the mountain, and line up a bunch of jumps all in a row. That way you always go off straight, making it easier to stomp jumps.
Then you have to do 5 different tricks and stomp each one. Normally i do a 180, s 360, s 540, then I have the last two huge jumps where I just spin alot. In case ur Gnarshmallow retarded stomping means you land going straight flat on ur skis. Spins are easiest to stomp because its easier to see if ur straight or not.