If he is still half asleep, all the better. Feed the baby in a calm, relaxed atmosphere, if possible. Loud music, bright lights and lots of action are not conducive to a successful feeding. Lying down to nurse sometimes works very well. If lying sideways to feed does not help, try lying flat on your back with the baby lying on top of you to nurse.
Gravity helps decrease the flow rate.
The baby may dislike the rapid flow, but also become fussy when the flow slows too much. This problem is made worse if the baby is not well latched on to the breast. A good latch is the key to easy breastfeeding. It is available without prescription, but fairly expensive, and works only occasionally. A nipple shield may help, but use this only if nothing else has helped and only if you have got good help without any relief.