I've toyed with the idea of those washer fluid heaters, but honestly have never come across a situation where I would have needed it. And the Model S nozzles are better protected under the hood lip than most. I do always use a premium -45C washer fluid.
I also pack a warm "work parka", hat and gloves in the car just in case, and just this year threw my winter-rated sleeping bag in the back. If I ever get stuck it'll serve as a warm blanket.