After collecting every objective coin, go to Shaun White and throw snowballs at him as many times as desired. Once you stop, your score will not drop until you start moving on your board then stop, or if you change locations.
When doing tricks downhill press SPACE and hold J + I until the trick completes. Repeat this while adjusting your position so you do not crash into anything. You will eventually get a x3 score and should have close to 100,000 respect by the end of the hill.