Stopping the ordinary guy on the street is putting a few paragraphs at the front and back encouraging them not to. Along the lines of the book is priced, this how I make my living, please consider .... etc.
ralph.m idea of generating the book on each purchase could be expanded. Leave a book purchased by so and so on such and such date where someone can see it and if they are going to get rid of it and pass it on they will.
Then add a hidden one, like in an exif file as part of a photo in the book.
I would circle back to the original question is old school. Technology has changed how books are made available to the purchasing customers. You used to have to print. You used to have expenses you no longer have. If you look at some currently successful authors they have a more if you find this book, helpful, informative, good, etc please make sure to purchase your own copy at ...
Many authors and artists are having success doing the be a part of the success. Be included in the community, be a supporter, etc. purchase a copy and be a friend on facebook, get access to a special newletter, get your review posted on a page, etc.
Make your customers your friends, goes a lot farther then taking a customers are the enemy attitude.