That works if you start with a warm canister. However, all canisters chill with use; it's just a property of liquids that vaporize into a gas (the fuel under pressure in the canister is liquid). If you use the stove for very long the canister will get cold from within, and a beer cozy might actually be holding the cold in. You have to really think when using canisters; they change as you use them.

That's why I like putting them in a tub of water. The water is fairly dense and will moderate temperature changes. If it's so cold that tepid water freezes rapidly, it's time to break out the liquid fueled stove or use a different canister warming technique.

HJ