I agree with feeding twice a day, unless there's a vet mandated reason for feeding more often (for example, I had to feed my boxer 3-4 small meals a day when I first rescued him b/c he had stress colitis). Also, for a picky eater, no snacks - period, until the dog starts eating his food. The empty calories dulls the appetite for healthier food.
You could also try wetting the food with low sodium, or no salt added chicken broth to enhance its appeal. I have also had luck with making a thin gravy using a spoon full of canned dog food and a little water mixed in with the food. I hope you don't have to keep your dog on the prescription food forever.
My current foster, Hallie, a very picky eater (shih tsu/pekinese?) wouldn't eat any of the kibbles my rescue director had me try: Nature's Recipe (grain inclusive or grain free chicken or salmon), Natural Balance grain free (duck or fish). I'm used to waiting out a picky eater, but she's the worst one I've had - lol. I finally broke down and fed her MY own dog, Maddie's, LID kibble, which she scarfs down: Acana Lamb and Apple. Sigh... Hallie knows the good stuff when she tastes it... I'm glad Hallie's only 12 pounds. I don't even feed this stuff to my own boxer - too pricey for my budget.