May be your understanding is wrong it seems to be, All programs, Function modules use PERNR details then eventually it calculates all related details in a sequence manner, When you are saying all pernr's in a single transaction i.e you may have to think about parallel program execution i.e Get all pernr's details and loop them to same program but they all should get executed parllely not in a sequence.
I hope SAP is having such provision to reduce progeam execution time.
Regards
Venkatesh