I've read Roger's several articles about using canister stoves in cold weather.
His solution is to invert canister, but that requires a heavier stove and maybe the valve gets clogged.
I've been thinking about alternate. There is lots of heat coming from the flame, just need to get a little of it down to the canister.
Piece of aluminum, 1.75 x 5.5 inch. 1/32 inch thick. Two holes in corner, #18 steel wire. 1.1 ounces total:

Assembled:

It's 21 F degrees.
Tried normal stove with almost empty canister (1/2 ounce left). It got really slow but did heat up water.
Then I tried it with the heater installed. Much quicker to heat up. Flame was much bigger.
Obviously, you only want to do this when it's really cold. Make sure canister doesn't get warm to the touch or it might explode. Stove and canister manufacturers are fainting if they read this…

