You can teach your dog to only take up food on cue. You could say like "take it" or "eat it" etc, and hand him the food to eat. Everytime he wants to take the food without your cue you give him a negative response (condition him to a negative marker, like "eeh too bad" etc). You'll have to practice the negative marker and taking on cue quite often until he learns it. You'll need to practice with different people too so he learns to associate that this applies to all people.