The Citroen DS4 tailgate release is operated by a handle / micro-switch arrangement that is incorporated into the trim that stretches across the tailgate. Citroen in their infinite wisdom have decided that no spare parts are available, which means forking out £100+ just to replace a tiny switch.
Our good friend Stuart from sunny Darlington has come up with a workaround that might just save you a buck or two.
Basically you are replacing the current lever with a Chevrolet switch. eBay appears to be awash with them. Just search "Chevrolet tailgate switch". Grab yourself a switch and follow the instructions: