This has come up before, and a number of us have learned to shoot both ways. My objective is the same as yours, to keep my body in better balance. For about a year, I would alternate days shooting right and left handed. I never got very good shooting left handed, but I did get very bad shooting right handed. I quit shooting left handed for accuracy every other day, and my right handed shooting has recovered. I still have the objective of keeping my body in balance, so I shoot a few arrows every day left handed, close to the target. I hold for longer than normal each shot, 5 - 10 seconds, since the main objective is strength and not to wear out my joints by shooting a lot of arrows. I enjoy it, I'm sure more than I would enjoy working out with left shoulder exercise equipment. Plus, it is fun to be reasonably competent shooting left handed so I can demo a left handed shot to left handed archery students.