There might be a market for keeping your keys on some service "out there". Boot your computer, type in your password, your computer sends the password to the key service. If the password is correct they send back the key, if the password is the destruct codes they delete the key.

No amount of hard-drive cloning will stop this. Paired with some other optional measures ("we delete the password unless you send an email every week" etc) and it's almost foolproof. You might still have a hard time arguing against destruction of evidence, though. I guess if your "don't delete the keys" email was "Please delete my encryption keys" you could be completely honest and they wouldn't believe you, resulting in your keys being deleted despite your complete cooperation.