Ok, so I searched for this but found nothing similar. Not sure if I should completely consider this an exploit, but I will leave that up to you guys.
I must say, this works better with the pvp guilds, but works with any guild with 8-10 people that are willing to try this.
First, you need two groups. Ideally, both groups will have 5 people each. Also, it would be recommended to have everyone on vent (or something similar).
Next, you have the leaders for both groups count down and queue for Battle of Gilneas at the same, exact time.
Over vent, both group leaders can see when the queue pops. If both groups get the queue to pop at the same time, everyone should enter. Otherwise, drop queue and repeat the process.
With a premade group of 10, you get around 10-12% guild xp per win, and you also get a bit of rep (not as important). Our guild does this every day to cap xp and its really easy. We usually get each match in less than 10 minutes, so that is a whopping 60% guild xp per hour. Most of the time, that is all we need.
Bonus: Once guild xp cap is removed, you can farm up a crap ton of xp to try and get server first level25 guild with this method if you have enough dedicated people. On my server, the queues take less than a minute or two.
Enjoy!