Great! This is your starting point. Do squats like that but keep pushing the boundaries a little. Try to decrease the external rotation a teeny, tiny bit, just to see if you can. Working on this is likely to be a long-term thing. It was for me. I thought I had it all worked out. Then I started doing Body Pump, which meant lots of squats under a 25-kg barbell. My quads didn't have quite the stamina I thought.
Completely unrelated ... I stopped off at a shop to pick up a few things on the way home from work. I saw a woman with the most horrible Trendelenburg gait. I wanted to tell her to go right home and do some clamshells. It was sad, actually.