Thank you everyone for your ideas. FBinNY: my original idea was to just cross the frame, as the housing doesn't look like it'd be too drastic a curve, but I just saw your second proposal on sheldonbrown.com/calipers. I think I may give mounting the brakes in front of the seat stays a try, it looks like (eyeballing) there shouldn't be any conflict, and I won't need to add any hardware to my bike. Thanks again.

Matthew