Yeah, neat idea!
One problem is, if it freezes you won't be able to get it off.
Anyway, ask and I shall do my best to obey : )
I couldn't find the right size lid so I got a container a little bit bigger - 0.5 oz
I put 100g (~3 oz) water in it. it started at 40 F but it was rapidly cooling from ambient air. 33 F after I heated the water in the pot for tea.
19 F and dead calm
Took 5 minutes to heat 15.6 oz of water from 10 to 95 C. 6 g of isobutane consumed. I'm drinking the tea as I write. I splashed up water onto the side of the canister a little.
I think a bigger container and more water helps. It get's cold from ambient air more than vaporizing the butane.
The water was not deep enough to contact the concave bottom hardly at all, so your technique might work a little better, but being able to splash water on the sides is good. I just used one finger and dribbled a little water. Also, there'de be less surface area to lose heat to ambient.
Anyway, in summary, I am underwhelmed by any of the copper/aluminum conduction techniques. I couldn't get the minimum temperature I could operate at reduced by very much, maybe reducing from 23 F to 16 F. And you have to experiment to get a configuration to work. Maybe a couple strips of aluminum and extend to the bottom of canister for more contact area. If this would work, it would be simpler than having to screw with water.
I think the container with water works much better. Maybe I'de use 4 ounces of water 1 inch deep. For each pot of water, I'de heat up 1 ounce more water than I needed, and put that in the container for the next pot.
And, maybe the best conclusion from all of this is to use inverted canister or white gas.
Uh oh - it's warming up - and it will be 10 years before the next stretch of cold weather like this in Portland, OR. Sunday morning I think it was below 10 F. Not quite an all time record (maybe 7 F?). And 3 mornings in a row below 20 F. I think I'll try walking across the swimming pool...