Technically you don't need to be in a premade to do this, but it makes it alot easier. After some experimenting in the game I believe I've figured out why I sometimes have 2-3 ret auras on in PVP at times, but never in PvE (or at the end of the match for that matter). You gotta enter the battleground WITH Ret aura already active. IF you die and turn it back on the benefits go away.
The most ret auras I've managed to get so far with this is 4. I've yet to make an all pally premade to see if we could get like... 20 for WSG or 40 in AV (That's a bloody scary thought... they hit you and take 4k damage from the staked auras), but I HAVE joined with others who have had it on and found that once in the game we had plenty of rets.