Pokud nechcete (explicitně) používat dočasné tabulky, bude to fungovat:
SELECT id FROM (
(SELECT 1 AS id) UNION ALL
(SELECT 2 AS id) UNION ALL
(SELECT 3 AS id) UNION ALL
(SELECT 4 AS id) UNION ALL
(SELECT 5 AS id)
) AS list
LEFT JOIN users USING (id)
WHERE users.id IS NULL
Je však docela ošklivý, docela dlouhý a pochybuji o tom, jak by fungoval, kdyby byl seznam ID dlouhý.