I have trouble with the overhead squat too, so I have not been doing it. When I try and squat down, my knees want to go over my toes, which is a no no. Maybe its a lack of hip mobility for me and posterior chain strength.
Hey Hunter, here is a video link I found through youtube showing how to do overhead broomstick dislocations.
YouTube - Shoulder dislocations
By the way - does your knees do the same thing mine does when using weight? I have also tried a one arm overhead squat with dumbbells and my body shifts to the side that I am holding the dumbbell on. I think for me its defiantly a lack of hip mobility. I am not sure about ankle mobility though because my toes are always straight ahead. I always look down at my toes before starting any lift to make sure they are lined up perfectly and adjust my feet position if I need to.