dhtmlx File Explorer

Hello all,
i have downloaded the file explorer demo and it works great. Here is my question:
In the config.php file, how can i use server root folders:
you have to use absolute path in config file
$gl_starting_directory = “d:/server/path/images”;

but i want it to read just from the server root. this way i can upload to my web hosting server.
$gl_starting_directory = “/images”;

how can this be done?

$gl_starting_directory = realpath("/images");
$gl_starting_directory = $_SERVER[“DOCUMENT_ROOT”]."/images";

Is it possible to read directory path from $_GET or $_POST ? or from Cookies ?