I'd say that a combo of talking with him about it and actively seeking peers for him so he gets a broader perspective than the big fish in small pond mentality may help.
There is a small but real chance that finding a bigger pond for a child will backfire. For instance, a child may not think much of himself/herself for being substantially smarter than their school mates. However, if you find them a select group of supposedly smart people, and they STILL find themselves to be substantially smarter than the "smart" kids... well, that could go to their heads.
