I had the characters sign a 4"x4" scrapbook, which was spiral bound, from Michael's. I intend to make a small scrapbook out of that with the picture of the characters signing and posing with Ds on the page that they signed. But I hadn't stretched my mind to what you are suggesting. But I think if you wanted to add the signature to a bigger scrapbook you could just cut out the page from the smaller book which has the right paper, and is the right size for getting autographs, and paste it into your other book.
Just an idea.