"Just 1 tooth" sounds silly, but "just the teeth that feel like they need flossing" doesn't sound as silly and is a lot more manageable because of it, IMO. And once you're in there doing those teeth, there's a good chance you'll do all of them.

And if you don't do them all, and only do the ones that you think need it, at least you did that much. It's certainly better than none.