UrlFetchApp.Fetch non standard port

Hope someone can help.

I need to return some data from a RESTful API service that is hosted on a non standard port 9091. I am using the following as a test harness:

var options = {
    'method' : 'GET'
  };

  var result = UrlFetchApp.fetch('http://testfetch.cmi.org.uk:9091',options);

  Logger.log(result);

And I recieve an error Address unavailable: http://testfetch.cmi.<?>:9091

If i changed to:

var result = UrlFetchApp.fetch('http://testfetch.cmi.org.uk:80',options);

The call works correctly. I presume that google block outbound traffic on non standard ports, is there any way to open a port as unfortunately I have no control over how the RESTful API service is hosted.

Any help with this much appreciated.

Thanks