I don't, but at one point last year when there seemed to be snow every morning I thought about it. I dismissed the idea because 1) it's a very specialty bike that I might only ride a handful times a year; 2) I found that unless there's more than a few inches of snow that I could ride my studded tires fine; and 3) if it got too bad I'd just take my car.

Riding 20 km on fat tires would be quite miserable, I imagine, as they probably roll as about as well as my studded tires.