[eluser]swhitlow[/eluser]
And here is how easy it is to include this externally in a PHP project that cannot be easily converted to a full CI project (which is the recommended way):
$controller = array('uri_string' => 'test','controller' => 'test');
require_once $_SERVER['DOCUMENT_ROOT'] . '/www/name_of_custom_directory/libs/controllers/index.php';
$inventories = $CI->get_accounts();
Where get_accounts is a function of the Test class in the test controllers directory.