Don't bother wih a secret override switch, just label one big button "START."
then connect it to the horn.
You'll know when someone stealing that *******...
That is a great idea.
I have a friend that worked for a local GM dealership.
He told me that they had accumulated hundreds of keys for all makes of vehicles.
They handled a large quantity of used vehicles, both trade-ins and auction purchases.
Whenever they needed a key, they would resort to their collection; and, sooner or later, would find one that worked.
The next time someone gets in the same kind of pickle, try around the dealerships and see if they also have a bunch of keys.
It seems to be common practice around here for dealers, both new and used, to keep a bunch of keys just for such circumstances.
In my own experiences, I have often found that a wrong key could possibly be made to work by inserting it and then pulling it back out partway, until you feel it start to work.
I have used this trick on vehicles, house-doors, and tool-box locks.
It won't work every time with just any old key, but it works more often than one would think.