Paperback books are not the only ones that give me trouble when I am trying to read hands-free. Most hardcover novels, even those that have circulated through the library system for a long time, simply won't lie open to a particular page.
Someday, I intend to create a book weight, but until then, I took a clue from my hands-free paperback book holders, and came up with a very simple solution for hardcover books.
All you need is a piece of elastic cord, tied in a loop. With your book open to your page, hook the loop of cord around the upper left corner and stretching it across the back of the book, hook it around the lower right corner. With any luck, it will be just enough to hold the book open, even if not quite perfectly.
Update: see this post about using my paperback book holders to hold hardcover books... sometimes the above trick does not work well enough: using-hands-free-paperback-book-holders