The 2nd key can maybe send the BTC to an another wallet ? So they can't acces to the coins anymore...
That would be great, but how do you achieve that without internet connection, and without any code being executed from inside the wallet?
Easy, something like twilio to grab all SMS messages, and react on either any message being sent, or a specific message being sent. I guarantee you someone in jail can find a way for someone to send a text.