In the bait and register approach, sn user will be allowed to ask a question or add an answer without any prompt for registration but on submitting he will be taken to the registration page with a message asking to register in order to post. If you happen to give a simple registration form or Facebook login, the user will do another click get registered and whatever he submitted will auto post.
I have this setup on Wordpress WMPU QA and it worked very well for me. But Q2A does not provide such a feature and if someone is a hacker here please let me know how to implement the same. I understand it must be some sort of a post capture and verify for user loggedin then redirect to register then back to form to submit logic.