When you say kill switch do you mean a simple battery power switch much like you would find on a racing car to isolate power?
The thing is the immobaliser system in your car is more than enough to prevent it being stolen, if someone can bypass the immobaliser then your switch will take seconds to traverse.
If you are still concerned then Talk to your dealer they might be able to fit something suitable without costing your warantee. Or consider a steering wheel lock or similar ?