Fetch images from API using Ember.JS

I´m getting into Ember.JS through Balint Erdi´s Rock & Roll with Ember.js , so far, so good....

Now I try to implement a new route in order to show band albums, including their covers, fetched from a public API.

I have this Album object:

App.Album = Ember.Object.extend({
    title: "",
    rating: 0,
    band: "",
    cover: null
});

I´m trying to fetch de cover artwork from the mediabrainz API. But the problem is:

How/When should I make the API calls?

When the object is being created? (despite user never ask for it)

App.Album.create({
   title: "The Headless Cross",
   rating: 5,
   cover: function () {
       Ember.$.getJSON(url).then(function (data) {
           // return ...
       });
   }});

At controller level? (didn`t work for me)_

App.BandAlbumsController = Ember.ArrayController.extend({
    albums: function () {
        var albums = this.get('band').get('albums');
        albums.forEach(function(item) {
            if (item.get("cover") == null)
            // API call using $.getJSON()...
        });
        return albums;
    }
});

At route level? (didn´t work either... undefined is not a function)

App.BandAlbumsRoute = Ember.Route.extend({
    model: function (params) {
        var albums = this.modelFor('band').get('albums');       
        albums.forEach(function(item) {
            if (item.get("cover") == null)
                // API call using $.getJSON()...
        });
        return albums;      
    }   
});

Could be cool if covers get fetched after user ask for the corresponding route...

Any ideas??

Many thanks in adv,

Ariel