Go through single-player Nationals and earn the Mils Mesas environment or earn enough points to buy it. After receiving this map, exit the mode that you are in and go to single player. Select the custom event option then go to "Nationals". Select the Mils Mesas track. Set the play mode to "Single Play", laps to "10", and number of opponents to "0". The MX superclass vehicle is recommended, but you can use an ATV or normal MX. Start the race and do not worry about time or anything else. Just do as many tricks as you can. Try Dingo Backflips+ and 360+ for quick points. You can get about 700,000 score points and 350,000 store points.
Activate the following cheats by entering the corresponding codes at "Options" > "Cheat Codes".
CHEAT FUNCTION - CHEAT CODE All bonuses - "YOUGOTIT" All challenges - "MORESTUFF" Freestyle tracks - "ALLSTYLE" All tracks - "FREETICKET" Paralyzer Monster Truck - "PWNAGE" All bikes - "ONRAILS" All riders - "WHOSTHAT" 50cc bike class - "LITTLEGUY" All machines - "MOREWHEELS" All gear - "WELLDRESSED" 1 million store points - "MANYZEROS" All in-game graphics for vehicles - "STICKERS"
Go to "Single Player Custom Event" and select "Freestyle" followed by "Ski Jump". You will be given a choice of two tracks. Select the second one. When you go down the ski jump, pop a wheelie and hold it. Somewhere near the center of the ski jump you should simply remain there until you stop popping a wheelie.