One of my highschool buddies handled tips like this. We'd sit down, he'd put a stack of dollar bills, usually 10-20 depending on the location. Then he'd sit another stack next to them. He'd then tell the server that one stack is the tip they are starting with and the other was the one that would be used to add to the tip IF he/she earned it. If the glass ever got empty, he'd take a dollar per glass from the first stack, set in the other. If it took more than a couple minutes to get ketchup or whatever, there went another dollar. At the end of the meal, whatever was in the first stack, was the tip he gave. We never had crappy service when with him now I know why