mixins_non-rest-route-action.js

import Ember from 'ember';

/**
 * use to support non restful actions on your api
 *
 * see more:
 * http://articles.jeffjewiss.com/non-restful-actions-mixin-for-ember-data-model/
 *
 */
export default Ember.Mixin.create({
  nonRestRouteAction: function (action, method, data, modelName) {
    const adapter = this.store.adapterFor(modelName);
    return adapter.ajax(action, method, {data: data});
  }
});

route.js

// ask for additional data to be sideloaded
  model: function (params) {
    var queryString = // code omitted here
    
    return Ember.RSVP.hash({
      model: this.nonRestRouteAction(getAppUrl(ENV, queryString), 'GET', {}, 'eligible-billable').then((result) => {
        return this.store.pushPayload('eligible-billable', result);
      }),
      matterTypes: this.store.query('matter-type', {active: 1})
    });
  },
  
  setupController: function (controller, resolved) {
    // resolved.matterTypes is set, but resolved.model is undefined
  },

serializers_eligible-billable.js

import {ActiveModelSerializer} from 'active-model-adapter';

export default ActiveModelSerializer.extend({
  normalize: function (typeClass, hash, prop) {
    return this._super(typeClass, hash, prop);
  },
  //http://emberjs.com/blog/2015/06/18/ember-data-1-13-released.html#toc_upgrade-guide
  isNewSerializerAPI: true
});