Task Manager Auditor / View Only Access

I have a requirement to setup auditor (view only) access within the Task Manager solution.  Unlike Account Reconciliations, there isn't a dedicated Role within the Global Options settings of the solution.  My initial thought was to assign an Auditor role to the "Viewer Group", however this would require every single task to have the role assigned.  

Does anyone know of a better solution, or do we actually have to assign the viewer group on all 2,000+ tasks? 

E.g., regarding assigning the auditor role to the viewer group.