I suggest that the existing procedures are adequate for this. If someone seems to be trying it on then we can tell them to change their username because misleading or disruptive usernames are not allowed. If they say that is their real name we block them anyway. No appeals. No trivia questionnaires, they're pointless because the celebrities in general know rather less about such silly details than their more obsessive fans do. I've seen two or three celebrities on Usenet use their real names online, amid thousands of people who thought that a username like "Washington Irving" marked them as real l33t d00dz. It isn't likely to be a major problem as long as our readers are aware that author identity is (as elsewhere on the internet) a rather fluid concept.