According to my copy of Panzer Colours, I'd go with YHR's suggestion. While only the elite (SS & Tiger II) units applied a winter camouflage paint job for the Ardennes offensive, the use of "snow camouflage was widely used on the Russian front"
There's not too many pictures in the book, but what there is looks like a watered down whitewash coat. Try a diluted coat of white paint applied with a cotton bud/q-tip/whatever you call "two blobs of cotton on a plastic stick" - I've had good results painting 1:72 scale German aircraft this way. In real life the winter camo was applied with whatever came to hand - which was usually something like a floor mop for regular army units (which is about the size of said "double ended cotton thingy" when you scale it down!).
Un-even random smearing is the best way I can describe the pictures I have, just keep the insignia clear. The book goes on to say (and show) that the paint adheasion was generally so poor that the crews could let it simply wear / flake off rather than re-paint at the end of winter.

let us know how it goes...
Mart