Cut a length of aluminum fence wire twice the page height. (Most any other type of wire will do but aluminum wire is easier to work with.)
At each end make a small loop around a pencil and then twist the short end around and around below the loop to end up with a sort of Hangman's looking noose. 5 to 10 turns should be enough depending on the weight of your book. Cut the excess off and use pliers to press the cut end closer to the wire.
Open the book and Insert the hanger rod between the back and the aluminum backing. Stop when 1/3 of the extended hanger rod is sticking out the head and 2/3 sticking out the tail.
Fold the rod over and into the indentation you made previously in the aluminum backing, toward the center of the book so that the hanger rod is caught in the indentation.