Heh, I found a way to slide down one of the gargoyle mounted ramps and into the arena without actually entering.
While there I seem to be invincible, also unable to attack anyone else, and the exit guardian offers me to enter the arena -
http://kiirani.com/stuff/screenshots...enterarena.png
I wonder as this is not gaining any advantage, does it qualify as bug abuse, it's pretty darn cool.