Absence management and FTE calculation

Summary

We are in the middle of implementing HCM (Rel11) and like to find a way to handle long absences and FTE

Content

In our organization FTE should go down to 0 when unpaid absence is more than 30 days of its duration. E.g. an employee will start parental leave, duration 6 months. This time period employee's FTE should be 0 on assignment. We are using positions and it would be vital that people on leave do not "reserve" the FTE that we allocate to someone else during the absence. Any best practices, help on this one?

Thanks,

Juha