Hi Martin,
I have suffered with this for exactly a year. It is gradually getting better but a year on, clearly this has been very slow progress.
I've just returned from a day mountain climbing in the lakes and despite slipping and sliding in the snow, it feels OK. my husband who is the climber really has this theory that exercises such as holding a raise or drop, like the one you have found, will help me. He suffered with tendon issues a few months ago and is convinced it was his climbing that made him better.
The question I have is, how long do you hold the raises and how many do you do? I am pleased that you have found something that helps Martin, its a horrible injury.
Beth