Tim, I have got lazy with having the sensors on the Leon, when shuffling around in car parks, I just wait until the buzzer goes constant then stop!
I fitted a set to the front of my Motorhome, I foolishly thought I could manage without a switch! First time out and really heavy rain caused the sensors to sound! I thought about installing a switch on the dash, then decided to use a microswitch operated by the gear lever, which switched them on when first or reverse was selected. My new MoHo does not have them fitted, however I have replaced the single rear camera with a twin rear camera and am going to deploy the redundant single camera to the front of the MoHo.
Having had VAG cars for over 10 years I realise a lot can be done by coding and have a OBDeleven device which plugs into the diagnostic socket to allow codings to be adjusted and switch on (or off) various features. I hoping this sort of device is available for MINI.