Add Primary flag in the Business title drop down

How to add Primary flag in the Business title drop down to identify the primary assignment on Add Absence Page

On Add absence page there is a drop down to show the business title for employees. In case of multiple assignments there are multiple titles in the drop down. Our client wants a flag to identify whether the assignment is primary or not. Please guide us if there is a way to show the primary flag along with business title in the drop down.