Yeah, I thought about it when it was talked about here before, but I'm not a fan of this idea. I can hardly make myself tell a child that if she eats the bread crust, her eyes will sparkle. My food program consultant started that one. I just don't think you will ever wean them off of it, and I also think it's part of our job to give them the right message.
Give them a little bit of each thing you make. If they want more of something, "sure, as soon as your plate is empty"
If they don't want to eat "ok, then I guess you're not hungry. You are excused"
the end!
You don't have to throw away food if it hasn't been on a plate. Wrap or tupperware, freezer, and serve again next week. If it's sandwiches, then make less to start with, and keep the ingredients out until the meal is over.