It does sound like a genius idea, but I don't know if it would work because mostly we just want to tell him we love him, if we have anything at all to say.
I say this because I made the happybirthdaymorrissey.com site for his 50th birthday and I found that most everyone just wanted to say that they love him. It's wonderful, of course, but I don't know if a whole book could be filled up with it.