The issue with soldering stainless steel cables [as I'm sure has already been mentioned...] is that you need to use flux, a torch, and silver solder. Tin/lead solder will not stick to stainless well enough to hold it on--and because a cable is inherently helical, all you are going to wind up with is a nipple that takes longer to fall off.

Spoke nipples crimp almost as readily as a regular cable end...