If you intentionally want to attack and miss, that's one thing. But the idea behind combat advantage is that your attack is serious enough to be distracting, which means it is serious enough to potentially damage an enemy, even if only on a 20. So no, I wouldn't think you can attack just to grant combat advantage and miss intentionally.
I'm new here, but when we only wanted to scare somebody, our DM allowed us to throw things at the empty square next to whoever we were trying to scare. His reasoning was that it had the same effect as an intentional miss, but the person on the receiving end wouldn't know that! Of course, we had to let the DM know this before doing it though.
This obviously doesn't deal with the "intentional miss to gain actual game mechanics" question, but it seems to work well enough for our uses.