How to insert a script into html pages before they will render? (Adobe Air 2)

Question

So I have a simple HTML pages browser in air (using Default one) I give it a link it renders out Page I use code like this (Flash builder)

<?xml version="1.0" encoding="utf-8"?>
<s:WindowedApplication xmlns:fx="http://ns.adobe.com/mxml/2009" 
                       xmlns:s="library://ns.adobe.com/flex/spark" 
                       xmlns:mx="library://ns.adobe.com/flex/mx">
    <fx:Script>
        <![CDATA[
            //
        ]]>
    </fx:Script>
    <s:TextInput id="uri" 
                 enter="browser.location = uri.text" 
                 text="http://www.apple.com/" 
                 textAlign="center" right="10" left="10" top="10"
                 toolTip="Hit &quot;Enter&quot; to go to url " />
    <mx:HTML id="browser"
             locationChange="uri.text = browser.location"
             left="10" right="10" top="40" bottom="10" 
             contentBackgroundColor="#E6DCDB"/>
</s:WindowedApplication>

Now I want to add to pages a simple script or any other html lines BEFORE page will be rendered with Browser. One like <h1> Hello World! </h1>

How to do such thing?