One of the aspects that the Starting Strength book emphasizes a good deal is that the wrists should be straight when doing the squat (see point 3, as well as the wrists of the guy in all the cartoons on that page). My problem is that my wrists always look like that of the guy in the image to the right on that page; they're severely supinated. In order to straighten them out, I have to either (1) move my hands farther out, which causes them to be bent inwards; severe "yaw", if you will, or (2) push my arms really far back, to the point of stressing my shoulder blades, and usually by the seventh rep my back actually hurts from the stretching.
Does anyone know of any stretches I should work on that will make this exercise easier? Thanks!