Stilly, what if you transferred the syrup to very small bottles for each person's individual use at the table? Then once your son uses up his "allotment" he'll either have to bargain with others for "their" syrup or do without for the rest of the meal. Of course, getting up from the table during the meal to fetch the big bargain bottle would be forbidden!

If that won't work, he can always be compelled to purchase his own big bargain bottle of syrup fom his own allowance or earnings. Then he can waste as much as he wishes... and may soon learn to wish to waste less. Frugality begins at one's own wallet!