Stroke rehab - arm over head

I'm been trying to figure out a way to easily lift my arm over my head, like I can do with my right arm. Standing up I can get my left arm to shoulder height with tons of concentration and a slightly bent arm due to bicep spasticity.  Lying flat on my back on my bed I can raise my arm from the side of my leg to pointing to the ceiling and then over my head until it almost touches the bed above my head. I can do this dozens of times, no problem. So I thought maybe fixing some spasticity would help. That took the form of trying to keep my arm straight above my head while lying face down on the bed. After 5 minutes in that position my shoulder muscles were screaming.
Someone has to know the answer. I've also tried 8-12 lb.  handled medicine balls when I still went to a gym. The idea being, trying to swing it forward and backward until you can do a complete circle. Just like you swing cowboy coffee to settle the grounds. I've substituted a gallon jug of laundry detergent now.
Don't try this unless your therapist or doctor oks it.