pg_dump: preserving oids in system tables?

Can someone confirm something for me? It seems that pg_dump with the -o
option preserves OIDS for user objects, but does not preserve the OIDs for
objects in system tables. Is that correct?

Is there any other way to preserve the OIDs in a system table? It would
make sense if that is not possible, but if it *is* possible, I would love
to know about it; it would make administering one of our databases easier.

(We have an in-house application that was developed in 2008 maybe? The app
has a table that associates a user (role) with a "department" by inserting
a row into a table with the values 'usesysid' from pg_user and a
department. It *works*, until you have to dump and restore. Then that table
ends up with garbage because the usesysids for each role is different in
the new database. At least that's what I have seen.)

I have requested that the developer make a change in the application for
future versions to use role names instead of the role's usesysid. In the
meantime, database major version updates require some manual intervention,
which is fine. I just wanted to ask in case there is a way to preserve
those oids that I'm just not seeing.

Thanks!

Natalie