For positions involving unskilled and semiskilled labor or for positions involving domestic, attending or other housekeeping and custodial services at state institutions or agencies or for other similar classes where the character of the work, or the place of work, makes it impracticable to secure at stated times a sufficient number of applicants to supply the needs of the service, or where it is impracticable to examine and secure such persons from candidate lists with sufficient promptness to supply the needs of the service, the Commissioner of Administrative Services may establish procedures which will permit the registration and, in his discretion, the examination of applicants, singly or in groups, at such times and places as meet the convenience of applicants and needs of the service, without public notice as required in this chapter.