Trouble is the cable is checked for operation during the test and that the compensator is working within its limits , I know what you are saying the old 106 rally school cars had no cable attached as they were just for off road , but the Ibiza I helped to run still had a cable and the plan was just to tighten it up when mot time came , but normally it would be slackened off to allow the hydraulic side to work first .

Piping is easy as long as you have a front / back split system as you just run the pipes in board , cut the single pipe and feed that into a sealed master cylinder then take the output out from the piston actuated end , all you are doing is when you pull the lever you are blocking the feed and pressurising the rear system .

If you have a differently split system then it becomes harder as you either need to use two hb master cylinders if still have abs , or loose the split and T piece them together in front of the single mc if not got abs .

Would think this might need a bit of "out of the box" thinking to sort it safely , would of thought some other calipers would of been a better long term choice tbh.