There's no need to; the password plaintext is available during the login process anyway. There's a difference between not storing it and not having it. All that

There's no need to; the password plaintext is available during the login process anyway. There's a difference between not storing it and not having it. All that would be required, really (assuming you don't want to store passwords, but are terribly, terribly concerned with the ability to extract a particular passwords under particular circumstances) is a conditional that shunts the plaintext somewhere before the login script/module dies. The login then continues as normal, but the bells and sirens go off and the plaintext password is available outside of the system. This, though, depends on user login after the fact, so to speak; turning over the hashes may mean more work for the interested authorities, but it won't depend on new logins.