So, this is EXACTLY like Athene's power leveling method for wow, except you don't have to have the higher level zone out. Essentially all you do is get a 50, or a group of 50's and a lowbie. (Within 4-6 levels of the instance) have the lowbie LEAVE the group and tag as many mobs as he can, and then have the 50(s) kill them. You have 60 seconds to kill the mobs everytime you leave the group.
He'll get full XP from the mobs. Enjoy .