Yes matey you can fit a reservoir to the hyd cylinder itself.....it will be a stand alone system with your independent rear calipers....Hornets7 is right though it should fail an MOT, as to comply you should have a mechanical form of park brake as well....some MOT testers turn a blind eye to this fact and it may pass but make sure you leave the car in gear if you park it on a hill cos with the hyd system alone it will, after the brakes have cooled allow the car to creep off down the hill....