protected function _getCustomIncludeFilename($position = '') {
        $key = 'custom_include_file';
        $key .= ($position) ? '_'.$position : '';
        return $this->_formatTemplate(
            Mage::getStoreConfig('turpentine_varnish/servers/'.$key),
            array('root_dir' => Mage::getBaseDir()) );
    }