You might consider changing your PHP configuration to add that directory to your include_path. Then you could include the file simply by its filename. If running on Apache, you can set this via a .htaccess file in your root web directory, something like:
php_value include_path .:/home/your_account/include
If that is not the option, you can call it as:
include $_SERVER['DOCUMENT_ROOT'] . '/../includes/filename.php';