I say, "All gone!" or "No more!" or any combination of those 2.
Then, I hold up my hands, palms toward him, while saying it.
Because I've done it always, when I do, he literally walks away to do something else, rather than continuing to be hopeful.
I do this with everything - dog treats, training treats, dry popcorn, etc.
It's funny that you posted this, as I was going to post something on this very subject after I was in a SD discussion on it. TGM's!
Love All Life, Thank You For Posting! :)