For me Yoga has been the main support to not having neck and shoulder pain. In the Downward Dog posture in yoga they teach you to drop your shoulders and bring your scapula bones down and in toward the middle. This is the same posture that works best on the bike, straight back and shoulders and scapula dropped down (toward your waist and lower back while on the bike with your hands on the 'hoods.' When I notice my shoulders are riding up and or my back is not straight I immediately do these simple things and all of a sudden the tension is gone and the straight back feels supportive to the rest of my core. Hope this helps. Any yoga book/teacher could help you with those subtle inward movements and gradually they become second nature.

Best of luck,

jpbayarea