Best (and safe, non-bannable) way to boost two mages using three 60 mages?

[MiRai]

I'm anxious about pulling dungeon mobs and dropping party before AOEing down -- blizz has banned a few notables for similar conduct. I'd rather something a bit safer.

I’m confused - why would Blizzard ban for this?

It's an obvious exploit of the system that's in place. The timer that's currently present is to help counter accidentally dropping from the group, or, in malicious cases, where a group kicks a player in order to steal loot, and it's not in place for players to repeatedly abuse for power-leveling their character(s) by dancing around the rules of tagging mobs and avoiding the penalty for experience gained while in a group.