Maybe I'm starting to show a little morbid fasicnation here, but when I was looking through the results of Grands Prix trying to find the Number 0 on a car, I found this photograph:
http://grandprixarchives.files.wordp...johnwatson.jpg
John Watson - McLaren, Brands Hatch 1985.
I can't think of terribly many instances where the number one plate has been driven by someone who wasn't otherwise entitled to it in F1, at least in modern time anyway.
I think I saw a photo once of Lance Macklin's HWM-Alta in '53 but can't really be sure.