Hi all, Cynosaur here. I've noticed this exploit in the game for quite a while, and it has yet to be patched up yet. Acquired from ICC 25m/25m H is a trinket called Deathbringer's Will - Item - World of Warcraft. The proc of this trinket turns you into a different form depending on what procs. When the different form procs, you're not able to mount up. You'll get an error message saying: You cannot mount while shape shifted.
Although it may say this, there's one form that it doesn't say it for. Whenever the strength procs, you'll get a buffed called Power of the Taunka, which will visually transform you into a Tauren. While under these effects, you are able to mount up on any flying mount, although you aren't able to use ground mounts. The size will stack with Deathbringer's Will - Item - World of Warcraft / Elixir of Giant Growth - Item - World of Warcraft. I have not tested this with Fras Siabi's Barely Bigger Beer - Item - World of Warcraft.
Pics:
http://i46.tinypic.com/zy8tjn.jpg
http://i47.tinypic.com/34pdoah.jpg
*Thread name meant to be DBW proc