You need to work with him more on the left. I believe (my opinion) that you should be able to do everything equally well from both sides. What I would do is start at the bottom, using whatever method you use, and get him used to you being on the other side. Start with leading. Once he does that, try pivoting. Once you can control the front end & the back end individually, try side passing. It won't happen overnight, it will take time. Go slow, be consistent. Keep in mind there may be physical challenges because he hasn't had to work that side as much. My guy doesn't like to bend to the (his) left, it's a suppleness issue. We work both ways, but I work to the left differently than the right because he needs more work building the strength up.