This might be one of those bad tcmalker's advice, but I'm going to recommend the ignition switch. Kill switch is for emergency so let's use it for that purpose. And when I say emergency, I don't mean 'Hey I'm about to crash, let me reach for that kill switch'. What you should be doing in that case is react and brake, swerve or do whatever you have to do to get out of that situation. I don't want muscle memory to kick in and press that kill switch, thereby voiding me of my chance of escape.
Emergency is 2 scenarios:
1. throttle stuck in open
2. already crashed, somehow throttle also stuck