I'm trying to think of what those might be. Assuming you already have employees and a payroll system, I think maybe only worker's comp insurance would be considered a fixed cost. Maybe the cost of a notebook computer or other device, if required. Employees who are less than half time usually don't have to be offered retirement plan options or mandated sick leave/vacation (although here in California, it might apply at all levels, I haven't checked).

Maybe the cost of a notebook computer or other device, if required. And business cards, if anyone still uses those. What else?

edit: possibly some training costs, depending a lot on the type of job and the previous experience of the worker