Is there some reason why you abslolutely need to turn cranks in the winter? I ended up burning out and hating biking for a few years because I felt like no matter what I had to ride and had to maintain some high level of biking fitness. When I got sick of dealing with clothing I bought a trainer and became a hamster. Finally I just couldn't do it anymore and quit for a while. Eventually I came around and started riding again because I do really enjoy it.
If you aren't feeling it, I say don't do it. Take the entire winter off, or else just leave the clothes and bike available should you feel inpired to ride at some point. If you've been riding a while and have a solid base you really won't loose much in a few months even if you do nothing at all. Seriously, I was suprised at how long after I was biking regularly I was still able to put a decent ride in on occasion.
If you feel you must do some kind of excercise, do something completely different than biking. Something that you are interested in or maybe haven't tried before. Myself, I really like yoga, but do what calls to you.
Then again, perhaps you'll find that once you do not have to ride, you'll realize how much you enjoy it. So remember it's not a job you have to do and there are other ways to excercise. Bike because you like to bike.