I am really pleased with the result.
This modification is invisible (from the outside and the inside) and completely reversible!
The whole thing took half a day, mainly because these cars are so extremely user friendly to work on. I mean, which other car lets you take the front grill off just by pushing four clips?
I bought an antilaser G9 parking assistant, which you can program for three different distances, all of which have three different speeds of beeping depending on how close you're getting to the obstacle.
The main unit was piggy-backed to the stereo fuse underneath the dash, so it turns on and off with the car, and everything disappears over the passenger footwell on the side. A little on-off switch was also attached to one of the existing holes under the dash (that switch is also invisible).
The sensor unit is attached inside the front grill and the cable goes through that radiator feeding air box (behind the grill), and follows the radiator fan cables into the area underneath the service panel.
From there, it goes into the passenger footwell through the new hole/grommet next to the main cable stem and attaches to the main unit of the G9 parking assistant.
Simple, invisible and reversible!