Interesting question. When there's a discount coupon or some other promotion, or when a dish is comped because of a problem in the kitchen, I tip as if I had been charged for all the dishes, since the server has done the same amount of work whether I'm charged for the dish or not. But when the dish is coming out of the kitchen unordered, the server is just carrying the dish out, not taking or managing an order. I think I'd tip only on dishes ordered--but then, since you're well-known at the restaurant, that's already a good tip, right?