If you know that he's vomiting on an empty stomach, you can somewhat help this by never letting his stomach empty. Offer him food at night before you walk him one last time and then feed him when he wakes up. Then again when you get home from work. You might even want to give him a bland diet when he has flare ups. Boiled chicken and white rice is a great choice (no bones, no skin). If this doesn't help, you can use plain cottage cheese or even jarred baby food meat (no onions or garlic). Some vets will recommend that you go so far as offering tagamet or pepcid (better than maalox) to help with reflux if this is an underlying cause.
This would be a good time for a fecal exam to rule out parasites as the cause of the nausea.
Let me know if you still have questions.
Pepcid is my favorite and the tabs are tiny so they are easy to give.
Here's the site that explains the dosage amount: