Changing navigator data in iframe with SlimerJS (or PhantomJS)

Question

By one trick or another I managed to handle headers in both new windows (window.open, target=blank etc) and iframes with SlimerJS. It is also possible to change navigator data (such as navigator.appVersion) for new windows, but I'm stuck with doing this for iframes. It looks like the onInitialized method works correcrtly only for main window and new windows, but not for iframes.

Here is some parts of the code.

var headers =
{ 
 "Accept-Language" : "test_language",
 "Accept" : "test/accpet",
 "Connection" : "keep-alive",
 "Keep-Alive" : "333",
 "Accept-Charset" : "test-utf",
 "User-Agent" : "test_ua"
}

var webpage = require('webpage').create(
{
 pageSettings:
 {
  javascriptEnabled: true,
  loadImages: true, 
  loadPlugins: true,
 }
});

_onPageCreated = function(childPage) 
{
 console.log('a new window is opened');
 childPage.settings.userAgent = options.useragent["navigator.userAgent"];
 childPage.customHeaders = headers;
 childPage.viewportSize = { width:400, height: 500 };

 childPage.onInitialized = _onInitialized;
 childPage.onNavigationRequested = _onNavigationRequested;
 childPage.onLoadStarted = _onLoadStarted;
 childPage.onLoadFinished = _onLoadFinished;
 childPage.onResourceRequested = _onResourceRequested;
 childPage.onPageCreated = _onPageCreated;
};

_onResourceRequested = function(requestData, networkRequest)
{
 for(var h in headers)
 {
  networkRequest.setHeader(h, headers[h], false);
 }
...
}

var _onInitialized = function() 
{
 this.customHeaders = headers;

 console.log("[webpage.onInitialized]");
 this.evaluate(function(options)
 {
  (function()
  { 
   window.navigator.__defineGetter__('appVersion', function ()
   {
    return options.useragent["navigator.appVersion"];
   });
   ...
  })();
 }, options);
};

...
               
webpage.onInitialized = _onInitialized;
webpage.onNavigationRequested = _onNavigationRequested;
webpage.onLoadFinished = _onLoadFinished;
webpage.onResourceRequested = _onResourceRequested;
webpage.onPageCreated = _onPageCreated;

I tried to do this with PhantomJS, but it seems like it is not possible to use "this" instead of "webpage" in the following case:

var _onInitialized = function() 
{
 console.log("[webpage.onInitialized]");
 this.evaluate(function()  // <<---not working
 {

 });
 console.log("test"); //is not being printed 
};

I would like this function to work with "this" object, so that it could be defined as onInitialized for both main page and child pages.

Anyway, the main question is about the SlimerJS code, not the Phantom one.