Ask question / give answer: only after log-in!

I intend to allow read access to a Q&A site I am working on without login, only if a user wishes to ask a question or give an answer (or execute a vote on a question or answer), shall the user be required to login (and login shall imply that the email address provided is valid and can be accessed by the user, either because the password is sent there, or an activation link).

In the Q&A plug-in, if a user
- enters text for an answer,
- then clicks "Login/Register and Submit"
- fills out the usual registration fields (possibly with a fake email address)
the answer is then accepted right away. What I would want instead is that the answer will only be accepted once the user has actually logged in (using activation link and/or password sent to him through email).

I am not too much of a Wordpress expert yet, so it may be that I am missing some relevant setting elsewhere... Nevertheless, any pointer will be much appreciated!

Olaf