My 7 1/2 month old only wants to eat what he puts in his own mouth -- how to get him to eat off a spoon again?

My son is almost 8 months old, and I have recently started giving him small bits of table food and cereal puffs so he can learn to feed himself. Unfortunately I think I created a monster. :-) Now he only wants to eat things that he feeds himself. He will clamp his mouth shut and shake his head if I try to feed him with a spoon. The problem is his coordination is terrible and he isn't able to get much food in his mouth yet -- either with his hands or with the spoon -- most of it goes in his lap. So if I let him feed himself he'll starve! How do I get him to let me feed him again??