Well, Rudy's book IS for sale in the Reagan Library gift shop. That should be good enough to qualify Rudy for president.
The way I see it, Nancy Reagan while a loyal companion to the President, was nonetheless a liberal Republican. Figure she authorized the Giuliani book to be sold at the Reagan Library. After all, Mrs. Reagan is a fan of liberal Republican Arnold Schwarzenegger. And probably a fan of Rudy too.
I heard that Rudy once stayed in a Holiday Inn Express, so that should qualify him as President as well.