for now you can strip the insulation off the ends of the 2 wires and touch them together to kill the bike. I found a bike like that and sparks came off the wires, the wire ends made contact accidentally once in a while.. and sometimes i got a mild shock when touching them together.. anyway, it is an ugly, temporary fix.
I bought a tiny round N.O.(Normally Open) momentary push-button switch at Radio Shack. The plan was to drill a mounting hole in the original switch body and epoxy the new switch into place... but i lucked out and found a switch off a junkyard bike so never went through with it..
Anyway, get any style of 2-pole on/off switch you like and solder the kill wires to it. How and where you mount it is up to you. There's no law that says the kill switch has to be where it is now instead of on the headlight housing or hidden under the seat.. or wherever. If you want to hide it, trace the wires back to any convenient spot and mount it there.