I think lightlysalted has the right idea, but I think getting together requires a group. And it seems the AOA is by far the easiest way to do that. I think the easiest way to do that is to have "mandatory" union dues. (Not to make anyone choke!) Of course you can't force people to join a union but here's the way i've seen it before: a pilot can elect to not join the union, but he/she will still pay dues. They just pay less, say 2/3. I know not all would agree, but it would make the union stronger as both the numbers become more acceptable and the money needed for bargaining would be available. I mean they negotiate (well or poorly) for you anyway. Seems fair to me.
I think lightlysalted's points are important if not necessary. Easier as a group but should be done anyway.