Simply not count them. That way it is no longer a race between 'who submits them first' (you know who you are ;)) so all the hangers on add their upvote. That's how this works. I suspect quite a few people have those sites in their rss feeds and as soon as they spot one they post it hoping to beat the rest to the game. It's the HN equivalent of /.'s 'first post' meme. Only here the 'first poster' gets rewarded with k…
By the way, I'd encourage you to post that data as a seperate post as my original didn't seem to get much traction and I think it's an interesting topic that should be presented to the community and the data clarifies exactly why.