This requires the help of a mage, and only works in outland.
1. Duel the mage
2. Get on your flying mount, but stay on the ground
3. Have the mage cast frost nova on you, then polymorph you
4. Once poly'd, have the mage channel a frostbolt on you while spamming cone of cold. If the timing is right, the nova will break at this point and you can hold down your jump key and swim through the air!
As long as you don't get back on your flying mount, you can swim around in the air until you zone or log. You can even get on your normal mount. Try this while doing Halaa PVP or killing mobs.
Video.