I made this same game over a year ago. It is in this thread http://www.unicyclist.com/forums/showthread.php?t=44975&highlight=
We started out as just doing one trick like that then we moved on to combos because it was more fun.
Jeff L. also made a different game where instead of just making a new combo, you add another trick on to the previous one. We got up to over 20 tricks in one combo, it was tiring.