Do you still have the neoprene carry case which was designed to fit the Optimus Crux stove into the base of the fuel cannister? You can fit an activated chemical hand warmer (or two depending on the size of the gas cannister in question) into the neoprene carry case and then attach it to the base of the cannister then put the cannister in an insulated bag (i.e. your sleeping bag) to warm up the cannister in very cold conditions just prior to using the gas stove.