Widget.xml (e.g. stored as file resource):

<iw:iwidget name="WidgetName" id="WidgetId" 
	xmlns:iw="http://www.ibm.com/xmlns/prod/iWidget" 
	iScope="xspScopeClass" allowInstanceContent="false" 
	title="Widget Title" supportedModes="view fullpage">
 	<iw:resource 
 		uri="http://openntf.org/domjs/dojo-1.4.3/ibm/xsp/widget/layout/xspScopeClass.js"/>
	<iw:content mode="view">
		<![CDATA[ 
<iframe id="_IWID_xspFrame_view" name="_IWID_xspFrame_view" 
	frameborder="0" marginheight="0" marginwidth="0" 
	width="100%" height="385" scrolling="no"></iframe>
<script>
var xspc__IWID_view={
   	xspComponentId: "_IWID_",
   	xspMode: "view",
   	xspProxyMode: "",
   	xspRunningContext: "iWidget",
   	_xspUrl: "http://openntf.org/Widgets.nsf/View.xsp"
}
</script>
<form id="_IWID_xspForm_view" name="_IWID_xspForm_view" 
	method="POST" target="_IWID_xspFrame_view" 
	style="display:none">
	<input type="hidden" name="xspComponentId" value="">
	<input type="hidden" name="xspMode" value="">
	<input type="hidden" name="xspProxyMode" value="">
	<input type="hidden" name="xspProxyUrl" value="">
	<input type="hidden" name="xspRunningContext" value="">
	<input type="hidden" name="xspTimeZone" value="">
	<input type="hidden" name="_xspUrl" value="">
	<input type="hidden" name="xspParameters" value="">
</form>
		]]>
	</iw:content>
    <iw:content mode="fullpage">
		<![CDATA[ 
<iframe id="_IWID_xspFrame_view" name="_IWID_xspFrame_view" 
	frameborder="0" marginheight="0" marginwidth="0" 
	width="100%" scrolling="no"></iframe>
<script>
var xspc__IWID_view={
   	xspComponentId: "_IWID_",
   	xspMode: "fullpage",
   	xspProxyMode: "",
   	xspRunningContext: "iWidget",
   	_xspUrl: "http://www.openntf.org/Widgets.nsf/Fullpage.xsp"
};
window.addEventListener( "message",
	function (event) {
		console.log('Received event: ', event.data);
  		var xpageiFrame = document.getElementById("_IWID_xspFrame_view");
		xpageiFrame.style.height = event.data;
	}, false);
</script>
<form id="_IWID_xspForm_view" name="_IWID_xspForm_view" 
	method="POST" target="_IWID_xspFrame_view" 
	style="display:none">
	<input type="hidden" name="xspComponentId" value="">
	<input type="hidden" name="xspMode" value="">
	<input type="hidden" name="xspProxyMode" value="">
	<input type="hidden" name="xspProxyUrl" value="">
	<input type="hidden" name="xspRunningContext" value="">
	<input type="hidden" name="xspTimeZone" value="">
	<input type="hidden" name="_xspUrl" value="">
	<input type="hidden" name="xspParameters" value="">
</form>
		]]>
	</iw:content>
</iw:iwidget>

To be added to XPage:

<?xml version="1.0" encoding="UTF-8"?>
<xp:view xmlns:xp="http://www.ibm.com/xsp/core">
<!-- add your XPages code here -->
	<xp:scriptBlock type="text/javascript">
		<xp:this.value>
			<![CDATA[	
var sendEvent = function() { 
	var height = document.body.scrollHeight;
	parent.postMessage(height + "px", "*");
};			
window.onresize = function(){
	sendEvent();
};
			]]>
		</xp:this.value>
	</xp:scriptBlock>
	<xp:eventHandler event="onClientLoad" submit="true"
		refreshMode="norefresh">
		<xp:this.script>
			<![CDATA[		
sendEvent();
setTimeout(sendEvent, 500);
			]]>
		</xp:this.script>
	</xp:eventHandler>
</xp:view>

To be added in domjs/dojo-1.4.3/ibm/xsp/widget/layout/xspScopeClass.js:

onfullpage: function sc_ov() {
 	this.displayMode(this.iContext.constants.mode.VIEW);
},