So I was in the middle of testing out a filter I made for no gcd and ended up finding this instead while trying to get out of combat while in the bank without killing the banker and losing rep with SW.
It requires a Rogue with SS. (Yeah another SS bug woohoo!)
Basically when you entered the bank go to the left banker set yourself to be at war with stormwind so he comes after you and walk directly back to the back corner. Once in the back corner put the banker in the corner and shadowstep.
You'll step right through the wall and drop down. The thing is you dont drop all the way down to the bottom tiles you just drop directly above street level.
Hit vanish to leave combat, switch it so your not at war with stormwind and feel free to run around the city. You can attack from here as well as i owned invading horde from under here.
The cool thing is i got the lovely "GM is appearing to your location" and the GM appeared on me but above ground so he couldnt even come underground to where I was. I set my status to AFK and never got banned. GM said I was afk somewhere.
I'd post screenshots but I have a gateway laptop and the print screen feature doesn't work like thatConsider the honor you could farm if you pulled this off on a Horde rogue.