B7 rear bumper hole drilling

[bkn]

My 2013 Passat Highline Estate is usually parked the drive at an angle of 20 degrees facing down the slope. Rain collects and settles on the rear bumper either side of the tailgate. On my B5 estate, 10mm holes drilled in the bumper allowed rain to run off. Is there likely to be a problem doing the same thing to the B7 Passat? Wires appear to run above the exhaust on the passenger side whereas the right hand side is totally enclosed with a plastic covering. I would prefer not to remove the bumper if at all possible.

Is drilling holes likely to affect the warranty?