Right, create your self a virtual user. Have this set with forwarding on and forward hunt group calls to the number you desire.
Then create a New huntgroup and call it overflow or the likes, make sure this is set to hunt, add the virtual user you have just created.
Then go to your group you wish to forward and add you newly created huntgroup into the overflow list.
Mess with your timers, till you are happy. JOB DONE.
ACA - IP Office Implement
ACA - IP Telephony
ACS - IP Office Implement (Aug 30th)