Here are some streches that you can do with a partner:
1. Lie down on your stomach, put your arms up on a raised surface (about 1 foot, crash mat) and get your partner to push down on your shoulders
2. Lie down on your stomach, get your partner to sit (not squish you) down on your shoulder blades to keep your body from lifting up, and take your arms and lift them up, you want them to grab at the elbows or below the elbows (part closest to your head)
3.Again lie down on your stomach, put your hands on your head, fingers interlaced, and get your partner to push your elbows together
4.On your stomach, put your arms by your side, and get your partner to lift them, towards your head. You want fingers to touch.
5. Sit in pike with your feet on a raised surface, put your ams behind your back, link your fingers together and get your partner to lift your arms and push you into a pike strech
6. Inlocate and dislocate: Hold a skippind rope in front of you, lift your arms over your head and behind you, all the way until they are touching your back. Then bring them back in front. Don't let go of the skipping rope. You want your hands to be as close together as possible. You could also use a towel, or rubber exercise band.
I hope these help.