How can I show a custom filter for unassigned technicians

How can I show a custom filter for unassigned technicians

Due to other limitations, dispatch all of our service requests by assigning them to support groups through business rules.  From there, our technicians will pick them up or they will be assigned by a supervisor.
 
For this reason, we need a view to show all requests that are not closed, assigned to a specific support group, and unassigned.  However, there is no option that I can find to select Unassigned.
 
As a work-around, I've selected "is not" and all of the technicians, however, whenever a technician changes, this Custom View must be changed.
 
Any thoughts? Does this warrant a feature or change request?
 
Thanks,
Adam

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