I've spent a lot of time searching for a quote that shows Wilson said Cheney sent him. I can't find it.
I won't rule out the possibility that Wilson was running his mouth with reporters early in the game and made that allegation off-the-record, though. Andrea Mitchell indicated that he was making that claim, but it's possible she doesn't actually remember the original allegation and is a victim of the media incorrectly repeating this over and over again.
I think it's a waste to use who sent Wilson in the "Wilson lied" argument because he did say publicly that the CIA sent him, not Cheney. The CIA is the one agency where nepotism is okay--better someone you've already cleared than someone you don't know. There was nothing inherently wrong with Plame recommending him--the only reason he seems to keep denying it is because he lied about it in the first place. He should have said, "Yeah, so?" and it wouldn't be an issue.
It needs to be hammered home that the whole reason Wilson was speaking out was that he claimed Cheney knew about his trip and his supposed findings. THAT's the big lie and the lie that needs to be debunked because it's the most damaging.