I'm not sure. There's lots of different techniques to try. First off...I'd wait a week after each refusal to feed. If you try to feed too often, you'll just stress the snake and it'll be anti-productive. It'll improve his appetite if he waits some.

--Make sure the mouse is very warm
--You might try a freshly pre-killed mouse...if you can bring yourself to do that
--Try putting the snake with the mouse in a small, dark container that is also warm and escape-proof (setting this container back into the snake's cage is the best way to do this) and then just leave them alone. Many balls are very shy eaters and will not strike/eat while being watched.