Brug VALUES() i en SELECT, der burde virke:
INSERT INTO employees (
company_id,
name,
position,
created_by,
last_modified_by
)
SELECT
(SELECT id FROM companies WHERE name = 'Acme Fellowship'),
name,
position,
(SELECT id FROM users WHERE login = 'admin'),
(SELECT id FROM users WHERE login = 'admin')
FROM
(VALUES -- all your new content here
('Frodo Baggins', 'Ring bearer'),
('Samwise Gamgee', 'Rope bearer'),
('Peregrin Took', 'Ent rider')
) content(name, position); -- use some aliases to make it readable