After a public hearing of which individual employees affected must be given reasonable notice, the director shall provide by regulation for the employment in any occupation, at wages lower than the wage rate applicable under sections 290.500 to 290.530, of such learners and apprentices as he finds appropriate to prevent curtailment of opportunities for employment. Such wage rate for learners and apprentices shall be not less than 90 cents less than the minimum wage established by sections 290.500 to 290.530. At no time may this provision be used for the purpose of evading the spirit and meaning of sections 290.500 to 290.530.