I have a simple Google Apps Script ContentService that emits a string like \"Hello world Sat Jul 14 2012 14:17:21 GMT+1000 (EST)\" The url is https://script.google.com/macro
I am not sure this is currently possible. We considered the JSONP method (which does work; I've tested it) but I don't think making an XHR against ContentService was ever tested. We'd probably need to set up CORS headers for this. Please file a feature request on the issue tracker and we'll see if it can be done.