express.js

import Fastboot from 'fastboot';

export default middleware(req, res, next) {
  const fb = new FastBoot({ distPath: distPath});

  res.render('foo-bar', function(err, layoutHtml) {
    const $layout = cheerio.load(layoutHtml);

    fb.visit(req.url).then((result) => {
      const app = result.instance;
      const html = result.html();
      const wormhole = app.lookup('service:wormhole');
  
      get(wormhole, 'holes').forEach((hole) => {
        $layout.find('#' + get(hole, 'to')).append(get(hole, 'html'));
      });
      
      // todo: also append the ember app!
    });
  });
}

service.js

export default Service.extend({
  holes: computed(function() {
    return Ember.A();
  }),
  
  register(hole) {
    get(this, 'holes').pushObject({
      html: hole.$().html(), // <- I'm sure line won't work
      to: get(hole, 'to')
    });
  }
});

wormhole.js

export default Component.extend({
  wormhole: inject.service(),

  _appendToDestination() {
    const ret = this._super(...arguments);

    if (typeof FastBoot !== 'undefined') {
      get(this, 'wormhole').register(this);
    }

    return ret;
  }
});