[Superman]

Crimp connections are hard to beat but if you make the individual connections in the same spot, then the whole mess is going to be much thicker than the rest of the cable. Small butt splice crimp connections are ideal I think, but you'd need the right connectors and crimping tool. Stagger the connections if you can afford to lose an inch or two of length. Individual tiny water tight shrink tubes for the connections and a water tight tube for the cable as the last step. Those connections would likely outlast the ones at either end.

Soldering is a poor splice method, IMHO. Hard to do, and not as reliable as a good crimp. But you know....it might work fine.