Just create a non-locked sub-forum to post in? Any time you make a post, an account is created for the username you used.
Another thing you can try is to remove
`&& !isset ($_SERVER['PHP_AUTH_USER']) ` from line 196 of
`start.php`, making it:
% if (FORUM_NEWBIES && !file_exists ($user)) %
Then you should be able to create accounts just by logging in to the locked forum. Though I have never tested what impact that may have.