Not sure if its an exploit, and couldn't find anything when I searched. If you fly into wintergrasp, you get a debuff that kicks you off your mount and gives you a parachute. I haven't tried it yet, but I did get dismounted and the parachute lasts until you land. I'm almost positive it'd give you credit for the achievement.
Hopefully it helps if your too lazy to jump off Scryers, or any other of the numerous ways to do it.