If, in any case, the prosecuting attorney and his assistants in a county in which there is a state mental health hospital are unable to act due to a burdensome number of cases brought under this article, the circuit court shall appoint some competent practicing attorney to act in that case. The court shall certify to the director of the administrative office of the Supreme Court of Appeals the performance of that service when completed and may allow the attorney a reasonable fee not to exceed the amount allowed for attorneys in defense of needy persons as provided in article twenty-one, chapter twenty-nine of this code. Compensation shall be paid out of the "Mental Hygiene Fund" provided for in section four of this article.