Ok, now I've never dived twins before and it's probably not going to be soon that I venture into that territory either, but diving twins and only using a drysuit for buoyancy control just somehow seems like taunting fate in some way to me.I am strictly warm water these days.
But when I used my dry suit regularly (it hangs in a lonely corner of the basement now) I never bothered with any BC. Get a basic hard backback and just use that. There is probably one in your ScubaPro jacket. Or buy one used somewhere if cost is an issue. I always had that sort of set up with my doubles anyway. All you need is the inflation in the drysuit.
If the drysuit has any neoprene in it you are going to float like a cork anyway.
I should mention that I dive my ds with my bp/w setup and only use the wing for buoyancy control because using the ds for buoyancy is just cumbersome IMHO. So the "throw out the BCD" idea is very much counter intuitive for me.
Can anybody give me a little more reasoning behind why a drysuit only would be considered sufficient and/or why a BCD should be used, if for nothing else as a backup for the ds?