partitioned table insert triggers

I'm trying to create a date-partitioned version of the postgres_log
table that is described here:
http://www.postgresql.org/docs/current/static/runtime-config-logging.html

In lieu of hardcoding the partition table names in the trigger, as shown
in the table partitioning docs, I wanted to dynamically compute the
table name. I tried:

CREATE OR REPLACE FUNCTION postgres_log_insert_trigger()
RETURNS TRIGGER AS $$
DECLARE
c text;
ptable text := 'postgres_log';
ctable text := ptable || '_' ||
to_char(NEW.session_start_time, 'YYYY_MM');
BEGIN
c := 'INSERT INTO ' || ctable || ' VALUES (NEW.*)';
EXECUTE c;
RETURN NULL;
END;
$$
LANGUAGE plpgsql;

I get:
ERROR: NEW used in query that is not in a rule
CONTEXT: SQL statement "INSERT INTO
measurement_postgres_log_2008_05 VALUES (NEW.*)"
PL/pgSQL function "postgres_log_insert_trigger" line 7 at
EXECUTE statement

I didn't really think that would work exactly for the reason given, but
I didn't know what else to try.

Now that my only idea is gone, the question for y'all is: how?

(Okay, I actually do have one more idea: construct the insert values
list with quote_literal. I'm hoping there's a better way.)

Thanks,
Reece

--
Reece Hart, http://harts.net/reece/, GPG:0x25EC91A0