Change the user and group that PHP executes as in Ajenti V

From http://phpsec.org/projects/phpsecinfo/tests/group_id.html

Change the user and group that PHP executes as. If you're using the Apache module, you'll need to change what user Apache runs as with the User and Group directives. If PHP is executing as a CGI, look at a method of executing CGIs as a non-privileged user like Apache's suEXEC or mod_suPHP.

How would one go about doing this using PHP FastCGI in Ajenti V?