I got the winter version of the JetBoil with the regulator last year for long backcounry ski days with the same idea -carry less water and make more whenever needed. The system works... sort of. Down to 20F or so you're good, below that I have had mixed results. You can boil water but the time definitely increases dramatically as it gets colder, at around 0F I haven't had much luck using an unmodified stove.
Hints: 1) Use new canisters. The pressure is greater thus giving the stove more ummph, plus the fuel is a propane/butane mixture and I'm told that at cold temperatures the stove burns the more efficient propane quicker thus functioning well for a while and then losing efficiency quickly. I use a canister a couple of times and then mark it with tape and hang on to it to use on summertime overnights or for boiling coffee water car camping. (Without going to far afield here the reason these stoves work on Mt. Everest is because the reduced pressure at altitude compensates for the low temperature.) 2) Use a windscreen. The directions say not to, but do it anyway. 3) Do a quick search online for directions on how to make a heat exchanger using 1/2" copper pipe. I do not officially recommend it and the stove guy at the local gear shop just shook his head, but people do it. I haven't had much luck using hand warmers to keep the canister warm.
Mostly I've found myself carrying all the water I need for the day when it is genuinely cold. If I were camping or it was critical that the stove function on command I would choose white gas in the winter. Good luck.