Search Criteria: Customers with tasks or no tasks...how????

In summary: I want my search results to show all people without a task, and then also people with a task (but filtered to the fields labeled "AND")

(( Activities: Tasks                 is empty              )          OR                

(Activities: Tasks                   is not empty                    AND
Task : Task Type (custom)      is Phone Call                    AND 
Task : Status                        is not completed   ))

Problem:  I cannot find a field that determines whether a customer has a task or does not have a task (what I labeled as Activities: Tasks).  The other fields are simple.

Does anyone know how to filter whether a customer record has a task or not?  Or a workaround, such as a simple custom field on the customer record?