I've only tested this in the Hyjal questing hub but I assume it's the same for every neutral zone with guards.
I searched for similar threads on the forum but didn't find anything, so I thought I'd share. Sorry if repost.
You'll need to spec Chi Wave since that's the key to the exploit.
Basically if you throw Chi Wave on yourself or an allied target it will bounce from you/your allied target to the enemy and you won't aggro the guards, it's really fun to use on level 80s who thinks they're safe by the guards.
As a level 90 monk the Chi Wave will kill them in one or two bounces.
Will post Screenshots if asked for.
This is my first thread on here so I'm sorry if the text is unclear or anything like that.