I have dual sided pedals and just switch to the flats with insulated/waterproof boots. Most of the winter I can get by with my winter hikers which, with wool socks, are good down to about zero for a couple of hours. My heavy boots are much warmer and about 4" taller and with wool ski socks will get me 3-4 hours to -15 or so, or about an hour at -40.

I would think it would be easier to convert a ski boot to an SPD style cleat than a pedal to fit a ski binding, but either sounds like a bodge.