I found the secret to this achievement! This may actually be the easiest achievement! On the map Airtime, stop before the last propellor. Inch over so you keep bouncing up. Hold a trick and continue flipping until you're at 20,000. Bail to the left on the ramp and wait until time's up. You won't lose the 20k and it will be applied to your score at the end. My video explains/shows you better!