Or it is how I just did it. Literally 5 minutes ago :-)
I sanded the area (a bottom of a aluminum coca cola can) with 60 grit, then 150 grit and finally 350 grit abrasive paper.
Quickly blew the dust off and heated it with a small propane torch. (Initially heated it too much due to how thin a can is so it turned dark almost blackish blue)
Keeping the soft part of the flame on it I dripped ordinary liquid soldering flux on it and after some seconds I could see the flux "wet" the surface. It seemed to help that i dripped it from a little height, maybe 15 cm up from the surface. As if the speed at which the drop hits the surface made it penetrate to the surface better.
As soon as I had the area I wanted, which coíncidentally is a circle of about 20 mm diameter 
, I hit it with ordinary rosin core solder.
It melted and balled up but after a little more liquid flux and a bit of poking with the end of the solder it also "wetted" the surface and spread out. I continued until my 20 mm circle was covered.
At this point I had some black ash like stuff floating in the middle and a center spot where the surface was not covered in solder. I dropped some more flux on it and heated a little more but it did not take to the surface.
I quickly put the propane torch down and used some 350 grit abrasive paper to rub that surface area while the solder was still molten. I had folded the paper so it was sort of stiff and I did not have my fingers any closer than 3 cm to the molten solder. It quickly adhered to the surface and I used the abrasive paper to wipe the ash like stuff off the surface.
Once cooled I scratched it with a screwdriver and it is really soldered to the aluminum surface. I found a piece of copper wire and soldered it to the surface covered aluminum.
I have been meaning to try this for a while because I need a cheap way to make a very much better thermal path from the copper noctigons to the cheap aluminum hosts than what even the best available thermal pastes or glues will do. Hell we all need that :-D
When I have time I will see if I can make a video on how to do it to a Jacob A60 host. But don't hold your breath waiting for it. I have 1000 things in my backlog of stuff to do that are not related to flashlights. Unfortunately LOL!
BTW: There are a number of reasons that this may not be a good idea that I can think of off the top of my head. The main reason is galvanic corrosion. Two dissimilar metals that are joined like this will have a corrosive effect on each other where one of them eats the other. But IF it is something that takes 10 years to happen in my 15 usd flashlight I DO NOT CARE. If the thing falls apart in 3 months you will get an update thread where I cry and whimper and look for sympathy :-)
