I did UR/Med Adv/Assoc Direc for a large-ish insurance company for a while as a part time gig. It was remote, they only needed me parttime as I was filling in while they looked for a full-time physician to staff.
That being said, I had NO experience in this before hand aside from getting ripped a new one every so often by the Case Managers or Hospital-Med Advisor guy. But as smokingmonkey said, it's networking and reputation (if I say so modestly). I ran into their director at some-function and we got along. Spoke to him a few times on the phone regarding difficult cases and while we disagreed, always remained cordial. Another physician recommended me to them when they were searching, met again with their director at another function and after two-three large glasses of wine and my mouth full of food he interviewed me for the position right there and then, and the rest is history.
They ended up offering me the full-time position, but I politely declined. Going into it full-time is not something I'm ready for yet but maybe in another 10-15 years.