Alexander Kjerulf, Chief Happiness Officer and author of a book about happiness, is asking people to evaluate his book. I like his approach. You might want to try something similar. Not only will he get some great detailed critiques of specific chapters using his approach, but he'll also be getting testimonials he can use on his book. A double win for him, but a win for the pre-readers as well because they'll get to see lhis book before anyone else AND be able to influence what goes in the book, or what comes out.
Check out his plea for help in evaluating his book at: http://www.positivesharing.com/2006/11/help-me-evaluate-