Instead of focusing on keeping your left arm I would focus on keep your right arm more straight. That way you won't have to much tension in your left arm and by doing some extensor action the left arm will straighten. Try this.
It is funny that you say that. The Handicap system is way to harsh. So I made my own short game skills test using some of those shots, but with different scoring and handicap. It has been really useful for my students. I have them take the test and keep the scores and re test in a month.
I find that my clients can make the biggest changes in their swing hitting into a net. Initially, it is a lot easier to commit to a swing change when you are not worrying about ball flight. After the change becomes more habit, then incorporate ball flight.