Awww, poor dude
I'd give him small amounts (a tablespoon or so) and give more when he's kept it down for a while (say, an hour or so?) Then slowly increase the amount and the time in between feedings until he's more or less on a regular feeding schedule. If he doesn't keep his food down, I'd take him back to the vet, or call them at least.
I hope that he's better very soon
