I think embedding //BIN in the print file (or an ESCAPE sequence, if not using GDI printing) is the only option that doesn't involve separate logical printers. Neither
SPOOL nor
EZSPL have any option for doing this via the XCALL parameters themselves.
However, both interfaces support the ability to specify a prefix file, so you could put the //BIN or ESCAPE commands in separate files (BIN1.PFX, etc.) and specify them in the XCALL statement. Which would effectively accomplish the goal without having to modify the code that generates print files. (But you'd still have to modify the XCALL statements to add the prefix.)