I know you said you didn't want a one-shot, my specialty, really. However, if I decided to write this (because I am enamored of the idea), would you still want to see? I think a prolonged story with this pairing would get mighty complicated, since Bellatrix doesn't really uhh... HAVE feelings, much less some to spare on a sniveling little boy, but I could definitely see her getting pleasure out of punishing him.
Anyway, I just might give it a shot.