Maybe try feeding some moist food. Could be the little guy is having trouble digesting the hard food.
Whenever vomiting crops up in my dogs, I feed plain white rice in small amounts until it settles down. I also add a Pepcid tablet about 10 or 15 minutes before feeding on advice from my vet - at least it's not as messy as Pepto!
Since he seems fine otherwise, meaning he's still active and still having an appetite, it almost sounds like a mechanical problem with the sphincter between the esophogus and stomach. The same kind of problem that can result in reflux in humans. Does he barf when he's been laying around the house, or after playing and exercising? That might be a clue to help your vet with a diagnosis.
Maybe you should try getting a second consultation with another vet.