[Exim] system filter pipe -- how?

I'm having trouble understanding how the system filter pipe command
works. I use pipes in other filter and also pipe transports -- I can't
work out how to make this work though! (No example in the docs that I
could find).

# main
system_filter = /etc/exim4/sysfilter
system_filter_user = 8
system_filter_group = 8
system_filter_pipe_transport = system_pipe_transport

# transport
system_pipe_transport:
        driver = pipe
        command = /root/bin/exim4_postgres_insert.pl
        ignore_status
        return_fail_output = false
        return_output = false

# filter file pipe line
pipe "<cmd> arg1 arg2"

Rory

p.s. Any cool way of sending header info to the database using a
persistent connection to postgres 7.4.x?

--
Rory Campbell-Lange
<rory@???>
<www.campbell-lange.net>