Populating large DB from Perl script

Hi.  This is a recurrent problem that I have not been able to find a
good solution for.  I have  large database that needs to be built from
scratch roughly once every month.  I use a Perl script to do this.

The tables are very large, so I avoid as much as possible using
in-memory data structures, and instead I rely heavily on temporary
flat files.

The problem is the population of tables that refer to "internal" IDs
on other tables.  By "internal" I mean IDs that have no meaning
external to the database; they exist only to enable relational
referencing.  They are always defined as serial integers.  So the
script either must create and keep track of them, or it must populate
the database in stages, letting Pg assign the serial IDs, and query
the database for these IDs during subsequent stages.

I have solved this general problem in various ways, all of them
unwieldy (in the latest version, the script generates the serial ids
and uses Perl's so-called "tied hashes" to retrieve them when needed).

But it occurred to me that this is a generic enough problem, and that
I'm probably re-inventing a thoroughly invented wheel.  Are there
standard techniques or resources or Pg capabilities to deal with this
sort of situation?

TIA!

kj