You have to cut rear brake line, connect tube from the main MC to the reservoir hole of the parking brake MC. Then connect high pressure side of parking brake MC with line leading to rear calipers. It works very well, so far I don't see any negative sides of this setup. Guy who fabricated it made many more pieces for local rally drivers, but they use it to block rear wheels, not as parking brake. They have bigger leverage of the brake handle and block rears effortlessly.
In the beginning I thought parking brake will not hold pressure for long due to internal leakages of the system. Now I leave my car on the hill for 5-6 hours, it doesn't move.
Feeling when I pull the handle up is different, it is very firm and makes 2 clicks only. I think for this purpose better to use smaller size MC with less displacement.
Vladimir, 89T