You can create a VirtualHost for each site which will allow users to have their own:
errors directory, //custom error pages
htaccess & htpasswd files.
Heres is a generator that will create a VirtualHost for you: http://wdguides.org/gusion.php?name=gen ... irtualhost
You must create the following folders in each DocumentRoot directory before apache will restart upon using this generator: cgi-bin, errors, and logs,