There were tele and wide adaptors made by Sun for various rollei's - not sure if they'll fit yours (I think they're usually bay 1 - they may not fit the larger lenses). They're not too badly priced, though I don't know what the quality is like - I've heard its not so great.
I picked up the 44 version for my baby rollei but haven't tried it out yet.
I kind of agree that the rollei experience is to enjoy them as they are. I got the adaptor to give me a little more flexablility (plus it turned up at the right price), but trying too hard to turn them into a "system" spoils the fun.