How to add add a page worker on intercepted page response

I'm building a firefox extension which intercepts a page load for a certain domain and returns it's own HTML instead. The issue I'm having is that once I've intercepted the page and returned the html, I can't seem to add a page-worker to allow the script to communicate back to the higher-privileged extension code. If there's a way to communicate back without a page-worker that'd be good too. Here's my code:

var { Class } = require('sdk/core/heritage');
var { Unknown } = require('sdk/platform/xpcom');
var { Cc, Ci, Cr, Cu } = require('chrome')
var observerService = Cc['@http://ift.tt/1efiEYk'].
                        getService(Ci.nsIObserverService);
var data = require("sdk/self").data;
var pageWorkers = require("sdk/page-worker");

Cu.import("resource://gre/modules/Services.jsm");

var TOPIC_MODIFY_REQUEST = 'http-on-modify-request';

var StartObserver = Class({
    extends:  Unknown,
    interfaces: [ 'nsIObserver' ],
    topic: '*',
    register: function register() {
        observerService.addObserver(this, this.topic, false);
    },
    unregister: function() {
        observerService.removeObserver(this, this.topic);
    },
    observe: function observe(subject, topic, observeData) {
        //console.log('star observer:', subject, topic, data);
        if (TOPIC_MODIFY_REQUEST == topic) {        
            subject.QueryInterface(Ci.nsIHttpChannel);
            let url = subject.URI.spec;
            if(!url.indexOf("https://example.com")) {
                subject.redirectTo(Services.io.newURI("data:text/html,"+data.load("intercept.html"), null, null));
                //This is not adding the page-worker
                pageWorkers.Page({
                    contentURL: "https://example.com",
                    contentScriptFile: [data.url("inject.js")],
                    contentScriptWhen: "start"
                });
            }
        }
    }
});

exports.Intercept = function(){
    var startobserver = StartObserver();
    startobserver.register();
};