Hi - I would like to help you out if possible but having a difficult time imagining what you are describing as far as arm restriction. Is there a common activity that you are unable to do 'normally' such as take a tray out of the oven using both hands palms up, pull on a door handle palm up elbow straight, reach seat belt etc. Can you move into your restricted position easily if someone else moves it for you? Did the physio say you had limited motion in the wrist, elbow or shoulder?
If it is just a matter of repositioning your shoulder then instead of holding it there all the time you might try moving it into the proper position only during those times when you need it. Practice repositioning your shoulder as you reach with your arm so your wrist and elbow work properly. It seems like a single scapular retraction movement would put you in the right place (pinch scaps together). Practice a little throughout the day. Lay off if the muscles get sore. Over time you should be able to teach the shoulder and arm to work together without thinking. Good luck.