I would invest some time to convert Replication object VEND_MAIN from simple to intelligent and see if the standard filtering fields suits your requeriment, if is a very complex approach I would explore add a custom FM in the table CRMC_BUT_CALL_FU (CRM) or (COM_BUPA_CALL_FU) (scn is full of discussions about this topic)
Of course you can allways put the filter on R3AC1 but this is too limiting for my taste.
Cheers!
Luis