I was on the roof of the Horde base with the Alliance flag and I was bored and decided to test some things out. If you find a wall you can wrap your camera angle around to have the golden gear to pick up the flag and you are in range for it.
You can pick the flag up through the wall, I have yet to find any real way to exploit this except to drop it in front of a wall and have a friend grab it to leave the enemy confused.