Since directadmin version 1.453 there is a great feature available for plugins. Since now (01.07.2014) plugins have the ability to run as a specified User:
As for plugin coders, if you wish to set any level to run as a specific user, you'd add any of these options to your plugin.conf file:
admin_run_as=user resller_run_as=user user_run_as=user
where you can set "user" to any value you wish, as long as it's not uid=0.
More details on the feature can be found here: http://www.directadmin.com/features.php?id=1594