Really, if you want to do this on 8x10", just use a half darkslide. Like 120, you'll get two shots per sheet/roll and you won't have the film flatness problem associated with rollfilm, and it's a simple, cheap solution. I made mine myself, but if you don't have a spare darkslide you can order one from Bender, pre-cut--

http://www.benderphoto.com/4x10pa.htm

Of course you can always crop after the fact. Art Sinsabaugh shot landscapes with a 12x20" camera and sometimes cropped to 3x20" or 4x20".

I've attached a photo showing how the DaYi 617 back attaches to a Tech V.