I did this all the time when we were defending WG. When I died, and I knew we were about to lose, I'd mount up (from the GY behind WG) and run off the cliff, levitate to the right and onto a building. There it was easy to make your way across to where you are standing in that first screen shot.
I'd AoE everyone below and kill loads of ally, it was awesome. But now in 3.2, it's completely useless, as they can just fly up on their mount and get you. By the way this isn't an exploit, there are many ways you can avoid a guard and still kill the opposing faction.