When you say only admins have access to the WYSIWYG editor, do you mean all other users have the plain text editor? Because in that editor, URLs are still converted to links, e.g. http://www.google.com
But to prevent Q2A from adding nofollow in the first place, you need to remove (or comment out) the first 3 lines I posted in the comment:
//$search = '/([^A-Za-z0-9])((http|https|ftp):\/\/\S+\.[^\s<>]+)/i';
//$replace = '\1<a href="\2" rel="nofollow">\2</a>';
//$html = trim( preg_replace($search, $replace, ' '.$html.' ') );
And don't add the other lines I posted there.