Leo says Gary could plug the wireless access spot into the Ethernet port he has nearby and then can connect to the AppleTV. Leo says an Airport Express would be really good for that. It'll then rebroadcast the signal to the AppleTV. He should make sure the Airport Express or the other access point is in "bridging" mode.
Another solution would be powerline networking, where he would use the house electrical lines to transport the data. It works pretty well now that they've worked out many of the bugs. But the in-wall Ethernet is probably the best bet.