I tried creating a synonym for just the package body. Users still could not see it without every identifier owner and package and package body:

owner = stage_owner
Package = RPT_CA_INVENTORY_AGING
Package body = GET_INVENTORY_AGING_SUMMARY

I want any user in the dB (who has the privs) to run without the owner:

SCOTT> exec RPT_CA_INVENTORY_AGING.GET_INVENTORY_AGING_SUMMARY;

instead of:

SCOTT> exec stage_owner.RPT_CA_INVENTORY_AGING.GET_INVENTORY_AGING_SUMMARY;