If you figure that out then let me know. Seems impossible to me. Maybe when brain scanning technology advances they'll be able to know what you're thinking.
You could be instructed not to disclose that you've given them the password.
So for example, you can be instructed not to tell your accomplices that their security is now compromised because every secret you had is no longer secret.
- the onus is on _you_ to "prove" that you don't know it or have forgotten it
- you can be told not to reveal that you've told them the password