cork 3's are super easy on tramps once you get em. Just think of throwing your feet against a wall in front of you, as wallisch says. Once you get the basic idea just focus on setting a three and dipping your shoulder a bit to go corked.
when i do my Cork 3's on snow, i always like to carve in REAL hard, and just carve into the direction of your spin, and just dip your forward shoulder and grad saftey, and that mommentum ussualy just sends you cork.
i learned them by trying them out of the end of half pipes. kinda hand drag it, almost wind up like youre going to do a Lincoln Loop, then kinda throw it sideways. youre never gonna learn it on a tramp. if you dont have a half pipe, then try hand dragging into them on jumps. hope this helps man! good luck!