Here is an easy one. Hasn't been tested yet, but you can have the illusion that you are doing a 3rd person snowboard game, with or without guns.

Theory
: Utilization of much of the area to work with will be needed and done in a specific way. You would start by making your weapons into your boarders. This will give you a decent charicter select mode at the beginning of your game.(see method of charicter select in car combat game example) Next you neeed to decide if you want the players to have obsticles like enemies to shoot or not. This will affect the way your models look. Have when the selection of player takes place have it give a universe register to the player that will affect the ending screen. Now on to the creation of the level. Start creating your level at the lower left hand corner of the work area. Do it in a long half pipe way and use the floor panels as angled floor with a strong slope force on it. Also make it as if it were ice. This prevents backward movements. Once again make it as if it were a long slanted half pipe to prevent veering off to the sides. When you reach the top of the work area have it get more narrow like a check point. At this checkpoint have a level switch take place that accually brings you a slight bit over and back at the bottom starting over again. This gives the illusion that you go from one check point and continue down the slope. Put obsticles like trees and rocks in the way with animations that cause damage upon collision. Also have flags or whatnot for the player to hit or go around in order to gain points through a universe register. This can easily be done with a console object. When copleted make turn left and turn right very obscure buttons that are hard to reach so that left and right can accually be straife left and straife right. We dont want the player to turn around and face backwards and travel up the slope. It's not necesary to make the player shoot but it could be an intresting way to do a trick. If you wish you can make a meter useing Ureg 125 that shows how many shots/tricks got off. Of course use the snow Ureg 236 where you need it.
Down side
: Aside from a lack of variaty of tricks, I can't think of any.