One option is to protect the master password with a security LARP scheme that's so complex and unwieldy that no sane attacker will believe you when you tell the truth. Like, Shamir's secret sharing, but the fourth part can only be passed via a Ballet choreography. Also, the sixth Yubikey is biometric and will only work with a latex fake of the right pinky prepared by this exact recipe. The final part of the password is the statistical expected value of this slightly unfair die, obtained after 10 000 throws, to the third digit.