This is a joke, but the person under duress also has to sell that they are under duress. This isn't something you can really "train" the average person to do on command.
It reminds me a bit of Jon Lovitz Pathological Liars Anonymous bit. "Okay! Here's the password...ya that's the ticket."
Duress password "1234", just make sure you have a very good backup and disable SSH password login. Anyone trying to snoop around is going to trigger it.
woD3PRBgELFHH9nuABH]ksD
Duress password:
duress123