application.js

var siteRoutes = {
    'login': 'layouts/login',
    'index': 'layouts/site'
};

App.ApplicationView = Ember.View.extend({
    layoutName: function () {
        var currentPath = this.get('controller.currentPath');

        if (siteRoutes[currentPath]) {
            return siteRoutes[currentPath];
        }
    }.property('controller.currentPath'),
    updateLayout: function () {
        this.rerender();
    }.observes('layoutName')
});