Aha! I've seen mention of this future CRX... Very good.
Well, my kill switch isn't quite
IN the shifter. It's inelegantly hose-clamped
TO the shifter. On the Firefly/Metro it was a "temporary" test installation, oh about 6 or 7 years ago.
Same thing with the Insight: hose clamp.
I will say however, that I actually did take care to ergonomically orient/locate the switch in such a way that the button falls perfectly beneath my thumb when I place my hand on the shifter.
Also, I routed the wires down through the flexible boot at the base of the shifter, and underneath the plastic housing. So it's not as messy as it sounds, and you should be able to do the same. And of course, you could modify the shift knob in some way so you don't have to use a hose clamp if you don't want to.