This may help someone out.
I was in spain and had left leaving back to the UK until the last minute (I ran out of money to stay any longer or go further) and winter was approaching, I had only summer gear and gloves and had to get across the pyrennees in cold and some snow on my MZ.
So I got some used 1 gallon or 5 litre water containers out of the trash dumpter and cut holes in them for my hands to fit in and for them to go over my bars and mirrors etc. I held them in place with duct tape and wire. I could work my levers perfectly well and these worked a treat. I wouldn't have been able to ride more than ten miles without them, as it was they kept the icey wind blast off my hands and kept them dry.
I still had a cold ride over the mountains and across France but I dont know how I would have managed without them.

You could always use latex ruber gloves under your main pair.. Always handy to have a few pairs for breakdowns, first aid etc