I don't understand why google can't do this now. It seems something simple for them to do. Maybe the programmers can do a copy/paste from the Adsense for content or search code.
I'd venture to say that the only people who know how difficult it would be to do it work at Google. I'd further state that every time I hear questions like this, it inevitably comes from either a non-technical person, or a programmer who's never worked on a serious project before. "Couldn't you just..." "Wouldn't it be easy to...." If I had a dollar for every time I heard those sorts of things, it still wouldn't be worth my time to try to solve every person's problems =).