Queues, Do Not Disturb, and Queue Fail Over

I need to get a queue to respond to a do not disturb setting. Here is my setup.

My receptionist’s phone:
line 1, extension 1, incoming route for 555-1212
line 4, extension 4, calls in a queue ring here

During the day if a call comes in and line 1 is available, it rings and it is picked up. If line one is busy, the call is routed to a queue where the user is give the option to hold, press 1 for whatever, press 2 for whatever. The queue only has one member, line 4. As soon as the line 1 call is done the receptionist answers the line 4 queued call.

My problem - if the receptionist goes to the bathroom or whatever unplanned event she is instructed to press do not disturb on her phone (polycom 550). When a call comes in on 555-1212 and the phone is on do not disturb, the call is routed to the queue where it is held indefinately.

What I want to happen, if the phone is on do not disturb, I want the queue to think it has no members and route the call to the queue’s fail over destination. Any ideas?

(I know she could subscribe and unsubscribe to the queue manually but that leaves too much room for error and pressing DND on the phone is hard enough to get people to remember to do.)