Anything that strengthens the rotator cuff would be helpful for paddling. Just google rotator cuff exercises and you will find plenty of ideas.

Here is a link to a PDF:
http://tinyurl.com/z2rmvwn

I did a lot of these exercises when trying to recover from a small rotator cuff tear. If you take the surgical tubing, tie a knot in the end, and shut it in a door, it will be a great way to anchor it.

Paddling was great rehab as long as I kept my hands 'in the box'. Anytime I started reaching up / high bracing I'd get quite a bit of pain. Try to use pain as your guide, avoid stuff that causes those instant flashes of pain.

Look in my 2016 photo folder. I uploaded the sheet that I used as a guide after I had shoulder surgery for a torn labrum. I used this with super light weight for about 6 months and then I worked the weight up (slightly). I do this entire routine after every workout, 20 reps each hand, through the 6 exercises. Let me know if you have any other questions.