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.