Neat idea, but entirely unnecessary in an Insight.
Doax has provided some members on here a custom shifter:
Mine has 3 buttons: Left - momentary, kills engine; Middle - toggle, clutch switch which disabled hybrid system; Right - brake switch, enables regen
The hybrid system will always automatically restart the engine, unless it's disabled or the car is in auto-stop. This is very friendly for new drivers because if they stall it, the engine restarts itself, and you can even drag the car forward with a stalled engine and get moving down the road again with electric alone.
-Using the injector kill method, you'd want to toggle the middle button to turn off the hybrid system, then press the left button to cut fuel and kill the engine. When the middle button is toggled again, the engine springs back to life, and you can then throw it into gear.
-Using Natalya's elegant forced auto-stop, you don't need to turn off the hybrid system. Instead, you hold the left button to send a ~2mph signal to the computer, then tap the right button to simulate braking, and the car will enter autostop even at 70mph. It will stay there until you throw it back into gear.