setting the Content-Type header with flash

content-type.mxml

<?xml version="1.0"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:mx="library://ns.adobe.com/flex/mx" xmlns:s="library://ns.adobe.com/flex/spark" >
    <fx:Script><![CDATA[
    import flash.net.*;

    public function sendStuff():void
    {
	var r:URLRequest = new URLRequest('http://www.youtube.com/foo');
	r.method = 'POST';
	r.data = '{wow what a great post body}';
	r.contentType = "application/whoknows";
	sendToURL(r);
    }
    ]]></fx:Script>
    <s:Button label="Send some stuff" click="sendStuff();" />
</s:Application>