sorry if this is common sense or a repost (searched, but didn't really know how to search for this)
basically this uses the idea than when you log off in a bg it doesnt kick you from the bg (although it will after the 5 minute afk timer), also this is really only useful to apply to ~5 characters (less will make this less useful, more will make this more difficult)
Step 1. DISABLE ALL MODS, this will make this trick MUCH faster and MUCH easier.
Step 2. Place all characters next to desired battlemaster
Step 3-? Basically you have to go through all the characters, logging on, queuing/joining, logging off, then repeatedly logon then logoff rotating through your characters. keep in mind that you will have to re-logon to each character before their 5 minute afk timer is up. also when youre going through the first time to queue/join, you might have to start relogging before all of your characters have queued since it will take longer to queue/join than it will to simply logon/logoff. another thing is that with the exception of the first character, and maybe the second (and maybe the third and fourth ;P), the bg you are joining will need to have a very short queue, ie <30 seconds, the first one wont matter, and for the second one you only need to beat the afk timer for the first character. also while a fast computer/connection isnt necessary, it will certainly help.
now i know this doesnt seem to be that great of an exploit, but if you have a bunch of 70s like i do, this helps you get all of them pvp geared in the time in takes to get one of them pvp geared (you wont get a whole lot of honor, but you can trade the marks for it)