Hey Tim,
I am sorta ambidextrous as well, and took it on a challenge to learn left handed flying several years back before we lost our old pavement field. It was mainly so I could see what the fuss was about for overhead 8 entry doing the OTS pattern. Some people thought lefties had a huge disadvantage. Well, I am here to tell ya, I did it the period correct over the shoulder entry and was just fine. It's more about un-learning the other way of doing it, and since I never did it the other way lefty, I was fine.
Back to learning lefty - yes, use a junker, but I never crashed, and I did finally manage a full recognizable pattern within the third day flying session.
You know how you hold one hand over your head, and the other over your belly, and some people have a hard time doing them in opposite directions out of sync?
Flying is the same way! To learn, as long as your shoulder is good enough to hold your arm out a little and support it's own weight, have your right hand doing the same movements at the same time as your left hand. They will synchronize, and eventually, you will be comfortable enough to stop the mirroring and just fly with your left hand.
Try it, you will be amazed how much faster you progress.
Wish you the best, pain is no fun, I've had my share lately, don't wish it on anyone.
EricV