Data Security for HR170

We are trying to limit the results of the HR170 rport to specific departments. We have several departments per process level and would like to further limit the department.  For Process Level x, we have departments x, y and z. would like the report to only contain department y.  When a user runs HR170, the PROCLEVEL element group limits the data in the report to Process Level x but contains all three departments.
I've written rules on the DEPTCODE table so the Department dropdown in HR170 only shows the desired departments for the selected process level but if the user leaves the department blank, it reports on all departments.

Any suggestions would be appreciated.