Call Queue Primary User and Backups

Hello.  We have the following situation:

We have a call queue set up of our receptionist phone.  Most of the time our receptionist is the only person logged into this queue answering calls.

I would like to set it up so that when the receptionist is out that we can have it to roll to another sub-set of users and ring them all simultaneously.

Would like to do this without having to have anyone other than the receptionist login/out of the call queue. 

Any ideas of how to make it normally go to the receptionist and then in the event she is not logged into the queue have it simultaneously ring another group?  Is there a way to do this with group rotating?