When he is not in it gain access to his vehicle. With a sharp object render his speakers useless through the application of long slits in the cones. If they are repaired. Repeat, but add a generous amount of doe in estrus urine, fox urine and milk to the carpet under the seat, and in the trunk. Also pour a good amount into the foam of the rear seats and the defrost vents on the dash.

If your first efforts don't curtail his actions the second will make it very hard for him to sit in his vehicle and drive to work let alone listen to the stereo cranked up to 11.

You may have to continue this multiple times with subsequent vehicles until he learns, but eventually he will get the hint. Do this under the cover of darkness and don't get caught.