I have not done this personally, nor do I know anyone who has, but I have asked about it at a bike store and they seem to think it can be done. Get a fat bike with disc brakes (as they all do have). Then get a second set of narrow wheels, with the same cassette the disc brake rotors spaced properly, and for summer riding use the fat bike frame with the "summer" wheels. Supposedly the Pugsley uses hubs that are the same size as mountain bike hubs, so the scheme sounds good "on paper" as it were.