I was responsible for the first & last 15 miles of each day at my last dealership, everything else was business. Except for the paltry 33 cents per mile, it seemed to work out for the best.
But nmfaxman is right; the tech is going to find a way to even it out. Padding mileage reports, longer lunches, selling random parts/toner on ebay. It ain't right but, if you piss all over your techs, it happens.