I know this works for horde at least.
Sinse the new patch 3.0.2 you can mount up before the gate opens in Alterac Valley. Provided you run up to the gate as close as possible.
I did it on the right hand side of the horde entrance. Made starting that little bit quicker.
Just a side note - It appears that when compiling the patch, they have used an old version of BC. A load of bugs that used to work and were nerfed... Seems to have resurfaced. Maybe that can give anyone with half a brain and a few ideas to try a few old tricks.
Anyway hope it helps someone.