How do I bind XML node values to web service request parameters in Flex 3?

Question

I'm having trouble using values from an XML file as parameters for a web service request.

I'm using an HTTPService to load the config file:

<mx:HTTPService id="configService" url="config.xml" resultFormat="e4x" result="configLoaded(event)"/>

The XML file looks something like this:

<root>
<data>
    <wsdl>https://WEBSERVICEURL.foo/ws.asmx?WSDL&lt;/wsdl&gt;
    <username>ws_username</username>
    <password>ws_password</password>
    <clientID>1</clientID>
    <centerID>1</centerID>
</data>
</root>

In the configLoaded() method, I set the result of the HTTPService to an XML variable called configXML and set the web service URL to the value of the node wsdl.

private function configLoaded(event:ResultEvent):void
        {
            configXML = event.result as XML;
            ws.loadWSDL(configXML.data.wsdl);                               
        }

Everything works fine until I call the request:

<mx:WebService id="ws" useProxy="false" showBusyCursor="false">
    <mx:operation name="GetContactTypes" resultFormat="e4x" result="getContactTypes(event)" fault="getContactTypesFault(event)">
        <mx:request>
            <clientID>{configXML.data.clientID}</clientID>
            <centerID>{configXML.data.centerID}</centerID>
            <username>{configXML.data.username}</username>
            <password>{configXML.data.password}</password>
        </mx:request>
    </mx:operation>
</mx:WebService>

Instead of passing the values of the XML nodes, it passes the XML tags and the values, so instead of using 1 for clientID, it passes <clientID>1</clientID>.

Any idea how I bind just the node values?

Thanks!