Is it possible to add a non-user staff member for time tracking

Is it possible to add a non-user staff member for time tracking

I want to be able to track each individual staff member's time contribution in a project on Zoho Invoice, but I have no interest in making them users - this is strictly data collection for my use in determining staffing needs.  
Is there a way to add staff for time tracking without adding new users?  I've gone through everything I can think of... I'm hoping the answer is right in front of me.  Thank you!