I don't think you're going to find a camera much more compact than the folding land cameras (250, 350, 450, etc.). The image size is so big that you need some length to cover it. I think the pack film options can be summarized as:

The numbered land cameras
Mamiya Universal/Polaroid 600
Konica instant press (I'd love to have one, but too much $$$)
Medium Format SLR with instant back (RZ68, Bronica SQ)
Other press cameras/view cameras with instant back

What about a Holga with an instant back?
http://www.adorama.com/CZHPB.html