If there is sufficient demand, this might be implemented in a future version.
In the meantime you can achieve something similar by modifying function qa_question_create() in qa-app-post-create.php, as follows:
Change 'Q' to 'Q_HIDDEN' in the call to qa_db_post_create(...)
Comment out the call to qa_post_index(...)
Comment out the section if(isset($followanswer['notify']) && ...
Once you've done this, new questions will be created as hidden, and you can access them via the 'Hidden' panel under 'Admin' , and show them if you approve.