Greetings .... try pieces of trout/salmon fillet and chopped pinkies in a dish with a couple of lobworms chopped up. The earthworms should attract him to the dish and he may start taking other food. Slowly reduce the amount of earthworm and you should end up with a food accepting snake.
Some better pictures would be great for ID purposes. It looks like it could be a 'low-red' red-sided garter (Thamnophis sirtalis parietalis).