Hi, first time poster long time lurker here.
I was recently flying through Northrend only to find myself able to fly use abilities at the same time!
It's actually a very simple process
Fly into Wintergrasp from the Borean Tundra, it only seems to work when coming in from the Borean Tundra (I may be wrong)
This will also only work if when zoning into Wintergrasp you are affected by the Noggenfogger Elixer, skeleton form. (haven't tested with other transformations) You don't need the transformation to stay in the glitched mode, just to enter it.
You are also able to fly inside buildings you would normally not be able to.
This will not work in any other continent.
Good luck and have fun
Edit: Recently tested with the RAF Obsidian Nightwing mount, I was reduced to 110% speed, but still able to fly. Other mounts will give you normal flying speed.