Ok I've known this for quite some time and I thought it was maybe time to share it.
Hope it doesnt get nerfed to fast. (works for entering and leaving without deserter)
How to:
1. Make a new macro
/script AcceptBattlefieldPort(1, 1)
/script AcceptBattlefieldPort(1, 0)
2. Use it
---Important---
You must use the macro to enter the BG or it will not work.
To the people that have posted that this do not work for you; this macro isnt noob proof in the sense that you can just spam it and that it will work 100 % of the time. I find it best used with caution.
Somemore info it's effects
The BG icon dissappears 100%
You do get honour 100%
You do get marks 100%
You do show up on the scoreboard for other people and for yourself 100%
It seems that you will reserve one of the opposite teams slots so that you can play 16vs14 the reason for this is unknown but it has been suggested that it is beacsuse when one of the opposite team drops out your team will gain a reinforcement. Which would agree with my own experience