I went with the Tesla EPB. Jon Haas, aka Pantera-Electronics, can hook you up with what you need.
He offers the bolt on adapter, wiring harness, electronic interphase and on/off switch with location options. YOU can make it as simple or complicated as you choose.
It is very easy to install and you can leave your existing calipers and rotors in place. There are options you can do with it but changing rear calipers is optional. All that you need to do with the stock calipers is disconnect the cable system to them and flip them to the front for clearance for the Tesla EPB caliper. It mounts the best in the rear position.
I took the opportunity to update my rear calipers with something more practical using the original rotors but you don't have to.