So... is there such a thing as a banjo bolt plug? or a banjo bolt without the holes you could use to block off the fluid coming from the SMC/PVC hose at the rear caliper? Would be a little messy but would work I think for at least a roadside repair which disables the linked brakes but allows you to safely get back home for a repair.
Does that make sense?
Yes it does.
-- Number one would be to bleed off the pressure that has built up in the line to the rear caliper (initial braking pressure from the SMC plus all the pressure built up from the rear brake overheating). Better let things cool off first.
-- Then plug the line as you suggest
Then we'd have full functionality of the completely independent front circuit to the 4 outer, and the rear activating the middle rear and middle front.
Once we found out what the plug should look like, I'd like to keep one in my repair kit!
In Forest's case, there is a chance that no plug would have been required. If the very high pressure that trashed his rear brake was not able to push back the SMC piston, there is little chance it would have ever gone back at all, acting by itself as the plug we are looking for. Forest could have bled off the pressure to the rear and then the connection can be tighten again with little chances of the two outer on the rear ever activating again.