There are plenty of systems out there and very easy to fit provided you don't want to cut the bumper cover. I never got round to it, but on the facelift 986s you could 'hide' the sensors in the aerofoil slot at the bottom of the bumper. Perhaps not full coverage but not far off.
I also found a camera that was small enough to fit into the cover of the rear towing eye, which would have been interesting alternative