Exemplo de uso de helpers em layout xml

Data.php

<?php
/**
 * PagSeguro Transparente Magento
 * Helper Class - responsible for helping on gathering config information
 *
 * @category    RicardoMartins
 * @package     RicardoMartins_PagSeguro
 * @author      Ricardo Martins
 * @copyright   Copyright (c) 2015 Ricardo Martins (http://r-martins.github.io/PagSeguro-Magento-Transparente/)
 * @license     https://opensource.org/licenses/MIT MIT License
 */
class RicardoMartins_PagSeguro_Helper_Data extends Mage_Core_Helper_Abstract
{
//  ...
      /**
     * Creates the dynamic parts on module's JS
     * @author Ricardo Martins
     * @return Mage_Core_Block_Text
     */
    public function getPagSeguroScriptBlock()
    {
        $scriptBlock = Mage::app()->getLayout()->createBlock('core/text', 'js_pagseguro');
        $secure = Mage::getStoreConfigFlag('web/secure/use_in_frontend');
        $directPaymentBlock = '';

        if (Mage::app()->getLayout()->getArea() == 'adminhtml') {
            $directPaymentBlock = Mage::app()->getLayout()
                ->createBlock('ricardomartins_pagseguro/form_directpayment')
                ->toHtml();
        }

        $scriptBlock->setText(
            sprintf(
                '
                <script type="text/javascript">var RMPagSeguroSiteBaseURL = "%s";</script>
                <script type="text/javascript" src="%s"></script>
                <script type="text/javascript" src="%s"></script>
                %s
                ',
                Mage::getBaseUrl(Mage_Core_Model_Store::URL_TYPE_LINK, $secure),
                Mage::helper('ricardomartins_pagseguro')->getJsUrl(),
                $this->getModuleJsUrl($secure),
                $directPaymentBlock
            )
        );
        return $scriptBlock;
    }
  // ...
}
    

pagseguro.xml

<?xml version="1.0"?>
<layout>
    <adminhtml_sales_order_create_index>
        <reference name="before_body_end">
            <action method="append">
                <block helper="ricardomartins_pagseguro/getPagSeguroScriptBlock"/>
            </action>
        </reference>
    </adminhtml_sales_order_create_index>
</layout>