How to set up a proper variant for process model?

I set up a process model for payroll process. In one step I include the 3PR store evaluation run (Program RPURMU00). I want to know how can I set up the variant for this program. This program requires to input Temse file as selection. But the Temse file number is different for each evaluation run.

And is PUST the only place to run process model for a regular payroll?

Thanks a lot.