SELECT fieldA, fieldB, fielbC
INTO temp_table
FROM dblink('dbname=dbname port=5432 host=a.b.c.d user=user password=pw',
            E'SELECT fieldA, fieldB, fieldC FROM data_table')
     AS temp_table(fieldA integer, fieldB integer, fieldC integer);

CREATE OR REPLACE FUNCTION archive() RETURNS trigger AS $$
DECLARE
BEGIN

    execute
    '
      SELECT fieldA, fieldB, fielbC
      INTO temp_table
      FROM dblink(''dbname=dbname port=5432 host=a.b.c.d user=user password=pw'',
                  E''SELECT fieldA, fieldB, fieldC FROM data_table'')
          AS temp_table(fieldA integer, fieldB integer, fieldC integer);
    ';

    return new;
END;
$$ LANGUAGE plpgsql;

INSERT INTO temp_table (fielda, fieldb, fielbc)
SELECT a, b, c
  FROM dblink('dbname=dbname port=5432 host=a.b.c.d user=user password=pw',
              E'SELECT fielda, fieldb, fieldc FROM data_table')
       AS t(a, b, c);

CREATE TEMPORARY TABLE AS
...