Wait for property in EmberJS on "server" side

In Ember, you can reference a property in a template, and the template will wait for that property to be populated before rendering.

This works great for obtaining a list of entries, which are populated by an external REST endpoint:

App.ItemsListRoute = Ember.Route.extend({
    model: function() {
        return {
            client: App.Client.create()
        }
    }
});

Where the Client constructor looks like:

App.Client = Ember.Object.extend({
    init: function() {
        var _this = this; // For referencing in AJAX callback
        $.ajax({
            url: MY_API_URL,
            type: 'GET'
        }).done(function(res) {
            _this.set('itemsList', parsedDataFromRes);
        });
    },
});

For my template that relies on the itemsList, this works great:

...
{{#each item in model.client.itemsList}}
      <tr>
...

However, I have another route for a statistics, in which I would like to do some calculations on the results of the request, and return those values to the template:

App.StatsPageRoute = Ember.Route.extend({
    model: function() {
        var itemCount = getClient().get('itemsList').length;
        return {
            numItems: itemCount
        }
})

I realize this is a contrived example - I could query the length on the template and it would work fine - but you'll have to humor me.

The issue with the above example is that the get('itemsList') is likely to return an undefined value, based on the data race of rendering the template, and the AJAX response and property setter being called.

How can I "wait" for a property to become available in my JS (not template code) so that it can be used to provide a model for the template?

Is converting the 'itemsList' property to a function returning a promise the most "Ember-Like" way of doing things? Would this heavily complicate my template logic?