The most effective way to wean a kitten off of formula is to do it, as the word wean implies, gradually.
The first step is to eliminate the bottle from the equation. Offer him formula from a bowl or saucer. Warm formula may be more enticing. Some bottle-fed kittens are happiest if they are held by a person during feeding, so experiment with that. As well, it may be effective to start feeding your kitten with a bottle, and then remove the bottle and immediately offer formula in a saucer.
Once your kitten is regularly drinking from the saucer, add increasing amounts of high-quality kitten food to the formula at each meal. Over time you should be able to eliminate the formula completely.
Most kittens are weaned by six to eight weeks of age. However, each kitten is an individual. A kitten that is not fully weaned at 10 weeks is not abnormal. Be patient and keep trying the tricks above. Eventually he’ll come around.
One final note: don’t try to wean your kitten forcibly by withholding the bottle altogether. If he refuses to drink from a saucer, let him have the bottle (but continue to employ the tactics listed above). A few extra weeks of formula shouldn’t hurt him.