A sharp, short little tap on the nose, with a quick, "No!" can help deter unwanted behavior.
It has to be right after the biting for them to "get it" and make the associations, and substitute the toy anyway, even if he's disdainful of it, to re-direct.
Those days of lithe, sleek, balletic adolescent kitty are sooo cool, though.
And so evanescent...as you're hearing, pretty soon he'll be filling out and plumping up and turning into Little Miss Muffet's Tuffet.
But that's cool, too....just a different kind of cool.
(Vicariously enjoying the growing-up-kitty stages here. My student's two little boycat critters just passed through this stage, it goes so quickly!)
Enjoy him in all seasons.
M.