Umm, unless you guys can Steamworks the key for me, no way.
I bought Sins retail upon release. Never picked up the expansions. Eventually had to move my install over to Impulse, which I never used for anything else. That got sold off, Trinity was released on Steam at a cheaper price than I could get the two expansions, and so that is my Sins install now. Sins sits comfortably with 95% of my games, and I like that.
I know Steam isn't everyone's fancy, but I'll pay the extra $10 to keep Rebellion neatly nestled in my games library if that is what is needed. Sad I'll miss the beta, but I'm ok with that as well.