Seconded! Another phrase (whose delivery might be hard to convey in text) is "Look, I dunno, but anyways..."

Maybe the big idea is to come across as not expressing much interest in the claim, instead of opposing the claim? I think most people are happy to move on with the conversation when they get a "move on" signal, and we exchange these signals all the time.

I also like that this is an honest way to think about: I really am not interested in what I expect will happen with that conversation (even if I am interested in the details of countering your claim.)