Well there are lots of great examples out there 🙂 So, let me give you some!
1. When Ryan Holiday had to promote the book launch for one of his clients, he uploaded lots of exclusive staff on torrent (he also knows some guys there as he mentions). So, what he won with this trick, is that by giving for free photos, videos, some chapters, etc. people learned about the upcoming book and also made them wait for the rest.
2. Another growth hack that again Ryan Holiday did, is that he sold an awesome book (Amazon.com: Growth Hacker Marketing: A Primer on the Future of PR, Marketing, and Advertising (APenguin Special from Portfolio) eBook: Ryan Holiday: Kindle Store) for just around $2.00 also using it as an up-sell medium for one of his other books (Confessions of a Media Manipulator).
3. Another common practice is to launch a landing page offering a pre-order through Amazon and also giving the ability of downloading some sample chapters. This way the author gets your email and can communicate later to you the book launch or any other offers he has. You can check an example of the Traction
Hope it helps.