I did it with Max by training him to do the "on trust" thing.
Oops, I only went to login, didn't realise it was going to publish the text.
Put a SMALL amount of food down, get the dog to sit some way away from it, and say "on trust".
Dog will try to get to the food, but keep taking them back and sitting them back down again. It takes a long time, and many attempts.
Don't put a full food bowl down, in case it gets past you and starts chomping.
But once the dog gets the hang of it, it realises that it doesn't need to eat every bit of food as soon as it goes out.
Which then leads on to it not needing to eat every bit of food it can see.