On offense or defense, just before WG is about to start, stand on the broken rubble of this downed wall from the last battle. When the wall comes down and goes back up, you'll get ported "out" of the wall and into a side area between the tower and the wall. Even if the wall gets knocked down during the next fight, you'll still be inside the part of the wall that's left.
Here's pics:
hxxp://imgur.com/UkKIn.jpg
hxxp://imgur.com/W1ejf.jpg
(Apparently my post count isn't high enough to embed links or images, so fix those links yourself)
I'd assume this works for other walls connected to a tower, but I haven't tried it.