As a starting point, you'd probably be best getting a bumper with them already fitted so it looks better. They are plastic bonded on the inside, hence look flush.
Integrating or enabling to the existing system could be more difficult. Not sure if they are just plug and play or if you need extra hardware. I suspect extra is needed as the cars with front sensors also have additional side sensors. You'd also need the firmware told to use them since the speaker beep front and back depending the source of the object.
Most people do seem to go for those kind of mods on the DS4, so will be a lot of try and see. It's the kind of thing I'd do, but mine has everything as factory fitted