Q & A: Answer settings for QA Visitor

I am wondering what is the proper setting to be able to show the answer input for a question in the front end of the site for a "QA Visitor" user type, aka unregistered user, but when they submit the answer they are redirected to a register page. After they are registered, the answer gets submitted in their name. I do have buddy press installed.

How can I make that workflow happen?