PostgreSQL 9.0 issues with function - postgresql

Question

Here is the function I am working with:
CREATE OR REPLACE FUNCTION f_multiply_row(_tbl regclass
, _idname text
, _minid int
, _maxid int)
RETURNS void AS
$func$
BEGIN
EXECUTE (
SELECT format('INSERT INTO %1$s (%2$I, %3$s)
SELECT g.g, %3$s
FROM (SELECT * FROM %1$s LIMIT 1) t
,generate_series($1, $2) g(g)'::text
, _tbl
, _idname
, string_agg(quote_ident(attname), ', ')
)
FROM pg_attribute
WHERE attrelid = _tbl
AND attname <> _idname -- exclude id column
AND NOT attisdropped -- no dropped (dead) columns
AND attnum > 0 -- no system columns
)
USING _minid, _maxid;
END
$func$ LANGUAGE plpgsql;
SELECT f_multiply_row('campaign', 'campaign_id', 50, 500);
Obviously PSQL 9.0 does NOT have the format method (introduced in 9.1), so I am trying to convert the method to work in 9.0 and am having the hardest time getting it to work.
Error : ERROR: function format(text, regclass, text, text) does not exist
LINE 2: SELECT format('INSERT INTO %1$s (%2$I, %3$s)
^
HINT: No function matches the given name and argument types. You might need to add explicit type casts.
So, I attempted to rewrite it in 9.0 style:
CREATE OR REPLACE FUNCTION f_multiply_row()
RETURNS void AS
$func$
DECLARE
_tbl regclass := quote_ident('campaign');
_idname text := 'campaign_id';
_minid int := 50;
_maxid int := 500;
BEGIN
EXECUTE (
'SELECT INSERT INTO ' || _tbl || ' ($1, $2)
SELECT g.g $3 FROM (SELECT * FROM ' || _tbl || ' LIMIT 1) t, generate_series($1, $2) g(g)'
USING _tbl, _idname, string_agg(quote_ident(attname, ', '))
FROM pg_attribute
WHERE attrelid = _tbl
AND attname <> _idname -- exclude id column
AND NOT attisdropped -- no dropped (dead) columns
AND attnum > 0 -- no system columns
);
END
$func$ LANGUAGE plpgsql;
SELECT f_multiply_row();
But, the above causes these two errors:
Error : ERROR: syntax error at or near "USING"
LINE 15: USING _tbl, _idname, string_agg(quote_ident(attname, ', ')...
^
AND
Error : ERROR: function f_multiply_row() does not exist
LINE 1: SELECT f_multiply_row()
^
HINT: No function matches the given name and argument types. You might need to add explicit type casts.