Get magento XML configuration for default, websites and stores

ConfigAsXml.php

<?php

// app/code/local/Ikonoshirt/Shared/Model/Adminhtml/

class Ikonoshirt_Shared_Model_Adminhtml_ConfigAsXml
    extends Mage_Core_Model_Config_Data
{
    protected function _afterLoad()
    {
        /** @var $xml Mage_Core_Model_Config */
        $xml = Mage::getConfig();
        $xml->loadDb();


        /** @var $result Mage_Core_Config_Element[] */
        $result
            = $xml->getXpath('/config/default | /config/websites | /config/stores');

        $output
            = <<<XML
<config>
    <default>
        {$result[0]->asNiceXml()}
    </default>
    <websites>
        {$result[1]->asNiceXml()}
    </websites>
    <stores>
        {$result[2]->asNiceXml()}
    </stores>
</config>
XML;
        $this->setValue($output);
    }

    protected function _beforeSave()
    {
        $this->setValue('');
    }
}

system.xml

<?xml version="1.0" ?>
<!-- app/code/local/Ikonoshirt/Shared/etc/system.xml -->
<config>
    <tabs>
        <ikonoshirt translate="label" module="ikonoshirt_pbkdf2">
            <label>Ikonoshirt</label>
            <sort_order>506</sort_order>
        </ikonoshirt>
    </tabs>
    <sections>
        <ikonoshirt_shared translate="label" module="ikonoshirt_pbkdf2">
            <label>Misc</label>
            <tab>ikonoshirt</tab>
            <sort_order>0</sort_order>
            <show_in_default>1</show_in_default>
            <show_in_website>1</show_in_website>
            <show_in_store>1</show_in_store>
            <groups>
                <config translate="label" module="ikonoshirt_shared">
                    <label>Config</label>
                    <expanded>1</expanded>
                    <sort_order>10</sort_order>
                    <show_in_default>1</show_in_default>
                    <show_in_website>1</show_in_website>
                    <show_in_store>1</show_in_store>
                    <fields>
                        <save_config translate="label comment" module="ikonoshirt_pbkdf2">
                            <label><![CDATA[Get config as XML]]></label>
                            <frontend_type>textarea</frontend_type>
                            <backend_model>ikonoshirt_shared/adminhtml_configAsXml</backend_model>
                            <sort_order>5</sort_order>
                            <show_in_default>1</show_in_default>
                            <show_in_website>0</show_in_website>
                            <show_in_store>0</show_in_store>
                        </save_config>
                    </fields>
                </config>
            </groups>
        </ikonoshirt_shared>
    </sections>
</config>