Custom session initializer for Ember Simple Auth...not currently working

customize-session.js

import Ember from 'ember';
import Session from 'simple-auth/session';

var SessionWithUser = Session.extend({
    user: function () {
        var userId = this.get('user_id');
        if (!Ember.isEmpty(userId)) {
            return this.container.lookup('store:main').find('user', userId);
        }
    }.property('user_id')
});

export default {
    name: 'customize-session',
    before: 'simple-auth',
    initialize: function(container){
        container.register('session:custom', SessionWithUser);
    }
};