class Shipment {
    private $_fedex_request = array(
        ...
        "RequestedShipment" => array(
            ...
            "ShippingChargesPayment" => array(
                "PaymentType" => "SENDER",
                "Payor" => array(
                    "ResponsibleParty" => array(
                        "AccountNumber" => null,
                        "Contact" => array(
                            "EMailAddress" => null,
                        ),
                    ),
                ),
            ),
            "CustomsClearanceDetail" => array(
                "DutiesPayment" => array(
                    "PaymentType" => "SENDER",
                    "Payor" => array(
                        "ResponsibleParty" => array(
                            "AccountNumber" => null,
                            "Contact" => array(
                                "EMailAddress" => null,
                            ),
                        ),
                    ),
                ),
            ),
        ),
    );
}

$ResponsibleParty = array(
    'AccountNumber' => Kohana::$config->load('fedex.currency.'.$this->_from_currency.'.billAccount'),
    'Contact' => array(
        'EMailAddress' => "name@domain.com",
    ),
);

$this->_fedex_request['RequestedShipment']['ShippingChargesPayment']['Payor']['ResponsibleParty'] = $ResponsibleParty;
$this->_fedex_request['RequestedShipment']['CustomsClearanceDetail']['DutiesPayment']['Payor']['ResponsibleParty'] = $ResponsibleParty;

$this->_fedex_request['RequestedShipment']['ShippingChargesPayment']['Payor']['ResponsibleParty'] = array(
    'AccountNumber' => Kohana::$config->load('fedex.currency.'.$this->_from_currency.'.billAccount'),
    'Contact' => array(
        'EMailAddress' => "name@domain.com",
    ),
);

$this->_fedex_request['RequestedShipment']['CustomsClearanceDetail']['DutiesPayment']['Payor']['ResponsibleParty']= array(
    'AccountNumber' => Kohana::$config->load('fedex.currency.'.$this->_from_currency.'.billAccount'),
    'Contact' => array(
        'EMailAddress' => "name@domain.com",
    ),
);

$this->_fedex_request['RequestedShipment']['ShippingChargesPayment']['Payor']['ResponsibleParty'] = array(
'AccountNumber' => Kohana::$config->load('fedex.currency.'.$this->_from_currency.'.billAccount'),
'Contact' => array(
    'EMailAddress' => "name@domain.com",
),
);

$this->_fedex_request['RequestedShipment']['CustomsClearanceDetail']['DutiesPayment']['Payor']['ResponsibleParty'] = Kohana::$config->load('fedex.currency.'.$this->_from_currency.'.billAccount'),
'Contact' => array(
    'EMailAddress' => "name@domain.com",
),
);

$this->_fedex_request['RequestedShipment']['CustomsClearanceDetail']['DutiesPayment']['Payor']['ResponsibleParty'] =
array(
'AccountNumber' => Kohana::$config->load('fedex.currency.'.$this->_from_currency.'.billAccount'),
'Contact' => array(
    'EMailAddress' => "name@domain.com",
),
);