Hi Don, sorry I didn't see this sooner, but we've been hosting the lovely PJ Swan from SanFrancisco the last few days.
My friend, luthier Glen Reid designed an instrument a few years ago that might fit the bill. Size wise it's in between a Mandola and Mando-cello. The scale is similar to that of a tenor banjo, it can be tuned many ways, has a flat back, and has 8 strings in four courses. Mine is the proto type, and has seved me well for 8 years. I know that the 12th Fret in Toronto has one of them (check their website...they'll be glad to send you a picture) or you could get in touch with Glen directly. (705) 382-5864)
Or give me a call (416) 690-8697 and I can fill you in with a few more details.