funny thing happened today while digging for parts. i came across a few broken throttle perches and wondered why the heck i would keep those, then it hit me. i have done this before, even on the older single cable models like yours.
few years back when the wife tipped my mtn viper over, she broke the kill switch. i remember when replacing it the new one came with a new sticker. the orange one that says push off/engine stop. under that sticker is a phillips screw that attaches that square push button to the switch mechanism.
so for fun, i tore a broken one apart and actually with a slight amount of prying, the assembly was easily removed. is the switch portion on yours broke or just the square button?
long story short, i was wrong on the older models, they do replace quite easily.