Redirect external URL to internal site or allow access to a URL without requiring authorization

I'm trying to shoehorn iPads into our enterprise network and my last hangup is with the iPads disconnecting the WLAN because it cant reach http://www.apple.com/library/test/success.htm.  

How can I either A) allow access to that URL without requiring that the user be authorized by TMG or B) redirect any request to that URL to a local server containing the success file?