More Half-Blood Speculation

I'm sorry to keep harping on this subject, but its just been sitting in my mind like a nut that I can't quite crack. I just finished rereading Chamber of Secrets and I've been working out a few things in my mind. Based on comments that Rowling has made, I'm reasonably confident that the half-blood prince is someone who's been introduced already. So I'm going to go through significant characters from CoS and my speculation on whether they might be the HBP.

1) Harry Potter - Rowling has already said that it isn't Harry.
2) Lord Voldemort - Rowling has already nixed him as well.
3) Ron (and all other Weasley's) - Pure bloods.
4) Hermione - Muggle born
5) Hagrid - I proposed Hagrid in an earlier post, but I'm beginning to lean away from that. First, Hagrid is half giant so he really doesn't qualify under the standard definition of half blood. I'm also against it now because Hagrid's parentage wasn't introduced until GoF. It would have been a stretch to shift those to CoS.
6) Snape - Snape is a popular choice, especially given that we're supposed to learn much more about Snape in book 6. I will concede that he is a suspect. However, CoS is the book that seems to have Snape in it the least. Under no circumstances do I get the feeling that Rowling might have decided to reveal something about Snape and then change her mind. I think this lack of focus on him hurts the argument.
7) Colin Creevy - Now, Colin is attacked by the basilisk giving us the idea that he's muggle born. He even mentions that his father is a milk man. However, it seems very odd to me that a family where both parents are muggles would produce two children who are wizards. Colin's brother, Dennis, appears in PoA. Given that, it may be that Colin's mother is not a true muggle. Either a witch who doesn't use her powers or a squib. Both are a little bit a stretch, but it leaves the argument open for something in the future. Of course, a counter argument would be that Colin is attacked first after Mrs. Norris and is absent for at least half of the book. Odd to have your title character disappear that quickly.
8) Tom Riddle - I know, he's Voldemort and we know that its not Voldemort. The thing is, Harry and Tom are the only well known half bloods. Tom also runs well through the narrative of CoS. Voldemort was very quickly shot down, but I've not heard anyone bring up the Riddle argument. This one could be hotly debated and without further evidence, it'll be impossible to prove. However, I think we should bear it in mind.

None of the other characters in CoS present themselves as good candidates. Their parentage is well established, or they're too minor of a character for open consideration. Without further information, I'm not sure I'll be able to ever solve the argument. Its a lot like the "who's going to die" game we had with OotP. But I'll keep looking for clues.