[Angib]

There is an official Mini kit for retrofitting rear PDC sensors so your dealer can give you a supply and fit price. It's not going to be cheap as the 'black band' plastic trim at the bottom of the bumper where the sensors fit has to be replaced by one with holes for the sensors.

You probably need to get the dealer to fit the sensors if you want the visual display as well as just beeping, 'cos it's bound to need the ECU coding for them.

 

[Angib]

The PDC retrofit kit must overcome the wiring problem since clearly it would only have been designed to be fitted to cars that don't already have rear PDC.

Here's the full RealOEM page with part number for the kit: