Backup of a big DB with a lot of large objects

We have a big DB that's backuped nightly using pg_dump in the custom
format. Most of its size are several thousand large objects. During
the dump of those LO the machine is heavily loaded so we are looking
for a way to "optimise" that part of backup process. We had an idea to
backup the DB but without the LO and to dump nightly only those LO
that were changed or added since the last backup. Unfortunately in
v8.1 (we use 8.1.5) there is no way to dump a whole database without
the LO.

Any ideas for a less taxing backup process?

--
Milen A. Radev