Hey bluenoser, I don't know your specific injury or how bad the rotator cuff is ,but allot of these will heal themselves,in time of course.
I work with a Guy who had surgery on his and was off work just about a full year,not for me as my pain was more of a hurts when I do that scenario ,so I don't high dive anymore ,but work was still a bit of a pain so I don't pull up as heavy of materials with a rope anymore either.
Allthough I believe exorcise is the oil for the joints , casting will aggravate the shoulder . You might try fishing runs that are a shorter casting distance from shore,also side casts with opposite arm might help too
I'm not going to recommend supplements for your shoulder pain, but I've been eating Cod or Halibut liver oil pills for years and found Recovery by Purica helps my shoulder pain,it's Just a personal opinion and could be a mind over matter kind of thing too.I believe it works so it does work kinda thing.Good luck to ya