I'm actually surprised this doesn't happen more often in the world of SEO spam. The obvious way to solve this is for the Google bot to give sites a Google refer

I'm actually surprised this doesn't happen more often in the world of SEO spam. The obvious way to solve this is for the Google bot to give sites a Google referrer string when it comes to index them. That way the bot would see those sites just as a search user does. Of course that means in the long run, Google bot would also have to pose with a fake USER_AGENT identifier to make sure it actually gets the real content.