Queue Overflow

I am trying to set up a queue (actually several) that will behave as follows:

When someone calls in, if a member of the group is at their phone, the queue will hold until the call is answered up to the timeout and then fail over to my answering service.

If all phones in the group are on DND, the queue will automatically fail over to my answering service.

I have several static members, but even if they are all on DND, the queue holds the call until the timeout. I have “leave empty queue” set to strict.

I can not have dynamic members because a person may be on the list for 3 or 4 queues and it is not reasonable to log in and out all the time.

How do I make my queue fail over if all users in the member list (static?) are on DND?

Thanks for the help!!