I think he might be Ritchie Coote in the book he is one of the beaters for the Gryffindor team and they described him as weedy. I don't think he can pull of a cruel look needed for Tom Riddle. It would be like Rupert playing Malfoy, it just wouldn't work. I don't think it's Cormac either I thought he was a sixth year like the trio. He looks too young for someone to make Ron jealous with.
Who knows he might be someone in the Slug Club too.