In some maps there are purple trampoline looking triangles on the ground. Drive as slow as possible towards it and you should get the achievement. It may take a few tries. From the Xbox.com forums:
"If you are doing the campaign, the first "human race" has a launcher that bridges a large gap...hit that at a decent clip and it can shoot you right into the edge of the arena (and get you your achievement)."
Also a lot of people are saying if you go off the triangle trampoline in a level (there are a lot) and then get shot in mid air you will get pushed up enough and get the achievement.