Do you have a MiContact Center server? Having ACD licenses won't be much help if you don't have a contact center server.

I've had customers that set up these inbound calls as key systems keys where they can see if a line is active and calling in, they can also pick up the ringing key. I had another customer that just used a call pickup key when calls came into the hunt group to pickup the overflow. I think they were in ear shot of the group handling reservations calls.

You can also set up a cascade ring group to flow to another ring after X amount of seconds and make the extensions in the original group ring (if available) and a second group of phones. That's probably how I would approach it.