Services that don't automatically assign a staff member

We have several services that we run - but want the ability to manually assign a staff member after people have booked in. 

Having a staff member permanently assigned to a service doesn't usually work. Having Bookings randomly pick someone is also not a good solution. 

Ideal scenario - all selected staff receive booking notification emails (they are also all then aware of how busy the services are), then one of those staff volunteer and assigns themselves to the service. Pretty simple, yet not currently available!