An employer who has registered and accepted the services of volunteers, student volunteers, or unpaid students, who are eligible for medical aid benefits under this chapter, may annually elect to pay the premiums and assessments due under this title at the rate due for one hundred hours of volunteer service for each volunteer, student volunteer, or unpaid student instead of tracking the actual number of hours for each volunteer, student volunteer, or unpaid student. An employer selecting this option must use the method to cover all their volunteers, student volunteers, or unpaid students for the calendar year.