Returning response from an asynchoronous call not working in Helper

An asynchoronous call in Helper is returning [object Object]. Here is JsFiddle.

App = Ember.Application.create(); {
  // put your routes here

App.IndexRoute = Ember.Route.extend({
  model: function() {
   // for simply showing the problem, I've put the instagram id
   // Actually I will parse the id from the post body
   return ['fA9uwTtkSN'];

Ember.Handlebars.registerBoundHelper("format-inst", function(input){
 // Add this part
 if (typeof input == 'undefined'){return;}

 function foo (URL) {
   return $.ajax({
       url: URL,
       dataType: "jsonp", 
  }).done(function (data){
       return '<img src="'+data.thumbnail_url+'">';                        
     var URL = ''+input;
     var r = foo(URL);
     return new Ember.Handlebars.SafeString(r);