Keep the battery as cold as possible (i.e. wet sponge).

Hadn't thought of that. I could stick it in the refrigerator for a while,
too.l


You can also build your own spot welder with a big fat
cazapitor.

Great! A man after my intellectual heart.


Search Google and YouTube for "capacitor discharge spot
welder". For example:
http://forum.allaboutcircuits.com/showthread.php?t=24385
If you don't want to build the entire circuit, just charge up the
biggest capacitor bank you can throw together.

I've got some electronic-flash caps lying around.


Last resort is to drag it down to Batteries Plus or some similar
vendor that has the proper spot welder.

I never thought of that! It might be worth a coupla bucks!


Very last resort is to just slop some epoxy on the flat wire and
battery terminal, and hope that it holds.

Unless it's silver-filled epoxy, no way.