Well i did, the trick was all to join into the same BG number when the window pops, but after that blizz removed the number and there were no more premaids for AV.
The other option was to all click at the same time and if everyone got the popup at the same time that was the BG we join, but it was not always 100% accurate and ~80% of the premade managed to join.
Guess i will findout that secret option in a week.