pl/pgsql FOUND variables and RULES

I have a volatile function (trigger) that gathers NEW.*, parses them, then inserts a
subset of values into a different table.

The table is set up as an inherited table where the parent table has a RULE :

CREATE RULE myrule AS ON INSERT TO mytable WHERE ( myfield >= 100 and myfield < 200)
DO INSTEAD
INSERT INTO mytable_100 (field1,field2,field3,myfield) VALUES
(NEW.field1,NEW.field2, NEW.field3, NEW.myfield);

Now when the trigger fires the insert does happen and ends up in mytable_100 but the
FOUND variable is not set (since technically 0 rows got inserted into mytable). Is
there a proper way to set up rules such that the FOUND variable is set within
pl/pgsql upon a successful insert (via the rule) or how can I check for a successful
insert?

Sven