Well, I was able to waste 1.5 hours on this today.
I made a mold in 2 halves out of aluminum, and they are held together with a screw.
The mold was suspended by a long screw held in the vise so the heat would not just transfer too quickly to the vise. I dipped the end of the cable in a liquid soldering flux, and then inserted it into the mold.
I then placed a small piece of solder into the bottom of the mold, and began heating it with a propane torch. When the solder began to melt I then kept shoving in more solder until the mold was full and stopped heating it.
When I tried to separate the mold halves....they were stuck together tight and it took one side in a vice and the other side I had to hit with a block of wood and a hammer to get them apart. The piece looked good and the cable was stuck in the piece really tight.
Well I tried and tried - but it was impossible to get the solder out of the second mold. It was stuck tight :'(
I guess I learned that solder does stick to aluminum! So...I will just keep making my cable ends out of brass, and them solder them to the cable.