Section 60. The personnel administrator shall cooperate with public and private colleges, universities and other institutions of higher education, which grant degrees and which provide facilities for educating students on the so-called ''co-operative plan'' of education whereby work-study programs are so developed and maintained that students enrolled therein may be employed in the service of the commonwealth in positions appropriate to their major academic interests. The employment of such students in positions classified under section forty-five shall be approved by the personnel administrator. The employment of such students in said positions shall, upon certification to the said administrator by a representative of such a college, university or institution that such student is enrolled therein under a ''co-operative plan'' of education, not be subject to the provisions of chapter thirty-one; provided that employment by the commonwealth of a student under such plan is for a stated and limited time.