I'm putting together a site integrated with WordPress. The following worked for me:
In ./qa-include/qa-external-users-wp.php: change line 44 to 'register' => '', to get rid of the register link in upper right of each page.
In lines 133 and 144 of ./qa-include/qa-lang-main.php, delete “ or ^3register^4” to prevent the registration prompt when viewing questions or voting on them.
Make the same change in lines 34 and 54 of ./qa-include/qa-lang-misc.php.
Make the same change in lines 42, 49, 64, 79 and 90 of ./qa-include/qa-lang-question.php.
I don't know how much this will help if you are not integrating with WordPress.