Ember.js: Load related multiple models

Since the ember-guides explains how to load mutliple models on a route like that

export default Ember.Route.extend({
  model() {
    return Ember.RSVP.hash({
      songs: this.get('store').findAll('song'),
      albums: this.get('store').findAll('album')
    });
  }
});

Im wondering how to load only the related model-entries from a second one, like loading ALL songs but only the albums which are indexed in the songs if we assume that the song model containing this

...
albums: hasMany('album'),
...

How can I do that?