Shared ODP question

I have a receivables statement program printing through a
externally-defined printer file; the program calls the invoice detail
print program (using a different externally-defined printer file).  I
end up with two spooled printer files and I'm trying to decide how to
get one (interleaved) file: statement, invoices, statement, invoices,
etc.

I can close and reopen the printer files so everything prints out in
sequence but I end up with a jillion printer files and the program is
slow (as you would expect).  I have customers
(transportation/logistics) processing between 1,000 and 25,000
invoices daily and performance matters.

I can embed the detail print code in the statement print progam but
that's more work than the plan allows.

I can convert the detail invoice print program to a service program (I
should be doing that regardless) but I think I'll need to have both
files' DDS in the same externally-defined printer file in order to get
one spooled file. This is probably the best design.

Is there some OVRPRTF magic I can use to eliminate any RPG coding or
am I stuck because of the externally-defined files?

Thanks,
Reeve