All you have to do is go to Shattrath city, in Flight Form, and enter the Isle of Quel'danas portal, and bam! You can fly! Be sure to abuse this, before it's hot fixed! Have fun! :>
I've yet to get off of the Isle, but I don't have epic flight form, but if I did, I think it would be very possible to get to the Undercity
Working and confirmed on 10-13-10
11:00AM EST
Proof:
Credit goes to: Some guy in trade