This isn't really a cheat but it looks cool. While playing ,in any mode, head towards a wall or object (not an ramp or 1/4 pipe. Lock into a manual then into a flatland trick (pogo, casper, ect...) by pressing and combo of Triangle, square, circle. (Example, to do a casper press square then triangle) Run into the wall/object hard enough to knock you out of the trick. Right away ollie (press X). Your guy will do a trick like he would get out of the trick you ran into the wall with.

In the menu edit tricks, put handstand double handflip as one of your specials. While playing ,in any mode, press the buttons to assigned to your handstand doublehandflip. Just before your guy stands on his hand ollie (press x)
Your guys will just do a double hand flip. You can experiment with any other flatland special and see the other cool unnamed tricks.