Hi greg,
here is an info page that could be useful for you: "Referential
Integrity Tutorial & Hacking" at
http://techdocs.postgresql.org/techdocs/hackingreferentialintegrity.php
But be careful, you have to deal with the system tables directly.
Have you tried selecting the data into a temp table and "copying" that
into the source_other_xref table? Could that be faster?
Ciao, peter