No, we didn't use a book. Our method was roughly this:
We got our son reading & reading and reading. And also reading to him. This started with Horrid Henry and Mr Gum, moved on to Alex Rider & Harry Potter and anything by Rick Riordan. This enhanced his vocabulary, and showed him how stories can be meticulously constructed. It also showed him how using words can be funny, or dramatic etc. Reading to (or with) them also helps them learn characterisation and how individual voices are different.
I think a camping trip where he and his friends started telling ghost stories at night made him want to start writing. And from there he really went off on his own without our intervention. He even wrote a 17 chapter "book"! After that, for the last 6 months, he had a tutor to fine tune him.
With DS2, the same grounding has been done, but he hasn't had the eureka moment yet. I intend to use something like the ideas presented here:http://www.kidsplayandcreate.com/50-pos ... -for-kids/
to hopefully kickstart him. Get him to choose a few and go for it. DS1 was so easy, that I'm afraid I'm pretty much in your boat now with DS2.