PL/PgSQL Question

From within a postgresql rule, is it possible to get at the values
specified in the WHERE clause of the query?

For example, given the query:

DELETE FROM map_tr_relationship WHERE fk_tr1_id = 4 AND fk_tr2_id = 5 AND
fk_tr_relationship_type_id = 1 AND from_tr_request_id = 4;

I want to intercept that query with a rule, and with DO INSTEAD call a
stored procedure and pass the values in the where clause to that stored
proc? Is this possible? If so, how?

Thanks for any info.

Brian Knox
laotse(at)aol(dot)net