Over the years I have had temporary issues with tendonitis. I've seen my doctor a couple times, but it never amounted to anything. For a few days I take some ibuprofen, adjust my workplace ergonomics slightly and the issue goes away.
A couple years ago I was having a bout of tendonitis, and I decided to mouse goofy. That is to say I switched my mouse to the left side of my keyboard. The first few days were very awkward, but I got used to it.
I also read this article on Lifehacker on why it is a good idea to mouse with the non-dominant hand.
The linked article on Lifehacker posits that doing this stimulate neural connections between the brain hemispheres. I don't know if I would go that far, but I haven't had a single flare up of tendonitis since I switched.
I find it fascinating that when I sit at my computer at home I immediately reach for the mouse with my right hand, and when I am at work I reach with my left. For me mousing with my left hand seems to put me in work mode.
Another Lifehacker article claims that you can boost your willpower and increse your stamina for focusing on tasks by brushing your teeth with your non dominant hand. I think I might try this some time just to do something different.
All on my own I came up with another non-dominant hand mind trick. Whenever I am warming up to play Ultimate, I catch with my left hand. Over the years I have gotten pretty comfortable catching with either hand. I started doing this since I found that there are times in a game where you can only catch with one hand.