I'm not at that point yet (years away thank god) but can you look at getting him some professional lessons, the instructor will snap him out of the 'i'm an awesome driver relaxation point', maybe the instructor can take him into the city and you can deal with him after that?

My mum wouldn't get in a car to teach anyone after my aunt put her through a letterbox when they were younger so my step dad and dad taught me, but i gained more knowledge from the instructor and prob saved them a small heart attack.