Aww John, what a dilemma. If it were me, I'd (despite any misgivings about negative reinforcement) make the door darting as unpleasant for him as possible. Use air horns, the hair dryer, spray bottle with water infused with citrus or citrus itself assuming he doesn't like those fruits. I'd stand by the door as though leaving, wait for him to approach and then shove the fruit under his nose or squirt him on the side or blast him with air. Anything to scare him spitless. Far far better than combing the neighborhood and putting up posters. If he isn't microchipped, I'd definitely get that done asap.