I recently had to solve this exact problem with zero budget and no time at all.
My workaround proved remarkably robust. I had to butt join two welding cables,
the light-gage kind used with smaller machines (don't know the number, sorry). I
cut a short piece of 3/8" soft copper tubing from the end of a roll I have, and
as it was tough to get over the wire, decided it needed the ends formed outwards
slightly like two mini-funnels on the ends. I took two 1/2" ball bearings, set
on on a bench block, held the short tube vertically touching the top of the
ball, put the other ball on top of the tube, and then tapped the top ball with a
hammer, driving the balls together. This did just what I needed, put a neat
little flare on both ends at once. Then I was able (just) to slide both
(stripped) cable ends into the opposing ends of the piece of copper tube. Then I
just put the tube in the bench vise and squashed it. It isn't particularly
pretty, but it seems quite strong. You may be able to see the joint in the
picture on this writeup, although a ground clamp is attached to it:

http://www.tinyisland.com/arcBlowFix.html

I don't know if this would work for the OP or not, but it worked well for me.

GWE