Was hesitant before posting this because I thought it was already posted =) But I searched and found nothing.
DISCLAIMER: I've only done this on my rogue while stealthed, but I've seen other classes do it as well (mage and pally)
When you're doing arena and you get the Ring of Valor map (The one where you start on a platform below the ground and you rise up as it starts), Start auto running towards any of the walls, and try to avoid the corner.
As the platform rises up, do not move at all. Press your auto-run button and then press W. Optional but I've always done it this way.
You should be running into the wall in one direction, not moving left or right. When the platform reaches the base of the gate, you should go through (80% chance I would say depending on how you do it).
I'll try to get a youtube video on it right now (March 15 2:05 PM) since I cant find an already done youtube vid.
=) Enjoy