You have to use either the Agency SUV or the Agency Buggy for this achievement.
To get this achievement, jump off the wedge-shaped rock near the Sports Complex, come from the road that leads to the Royal Vista hotel to get enough speed. Hold forward to flip twice, and make sure you land evenly.
Also, you can go to Cowell's building in Shai-Gen with a 4-star Agency SUV, ride the elevator up, and drive up the ramps until you get to the tallest inner level. Use the SUV's jump ability (hold ) to clear the fence, and you'll be good.