|Note: Of all the Special Tricks in the game, each riders unique stunt seems to last a about a second less than the standard shared stunts so your chances at this achievement are greatly increased if you use Up on the with both and first and then go straight into another stunt.|
Your best bet for pulling this off is on the second large jump on the Sandy Mountain track. Hit it with a bunch of boost and 100% pre load while holding down both the and . Since you press Up on the to pre load once you're airborne you'll engage your unique Special Trick right away, When it's near completion press the in another direction while still holding down the and to engage another Special move.
Also, it will be very helpful if you have an A Class bike with a high Trick rating. Level 2 shocks will make this much easier so use 'em if ya got 'em.