myfunc_setvar and postgresql 8.1

Hi,

For one app, I'm using the myfunc extensions described at
http://www.onlamp.com/pub/a/onlamp/2004/06/28/postgresql_extensions.html

This doesn't seem to work with PG 8.1. However in the discussion that
led me to use the myfunc extension, Tom Lane suggested there was a
feature in PG 8.0 that could do what I wanted (
http://archives.postgresql.org/pgsql-novice/2004-11/msg00119.php ) but
I don't know what feature was referenced, and I haven't found it in
the docs for 8.1.

Anyone knows how I could set session variables with 8.1? Or should I
adapt the myfunc extension?

Thanks.

Raph