I went to my PCP for my 6 month physician supervised weight loss. He was the one who referred me to the bariatric surgeon and knew what I was going through.
So I typed up my own letter of medical necessity. I had it in printed form and on a jump drive. I even had the receptionist print it on my PCP's letterhead. He could change it if he wanted or just sign the thing. He signed it. It was quicker, less work for him, and it said the things I needed it to say.