Yup, never ever use your hands or feet to play with the cat, or he'll grow up thinking that's okay.
The method I used with Assumpta (who was older and was a fear-biter) was to yowl like a cat, then physically turn my back on her and ignore her for a few minutes, like I was a littermate that she'd bitten too hard. The deliberate ignoring is what made the impact for her. She had good cat socialization and bad people skills, though...I don't know if it would work as well on a cat who wasn't pretty well-versed in inter-cat communications (like one separated from it's mom and siblings way too young). Might be worth a try, though.