An emergency interim successor is one who is designated for possible temporary succession to the powers and duties, but not the office, of a legislator. No person shall be designated or serve as an emergency interim successor unless he may, under the Constitution and statutes hold the office of the legislator to whose powers and duties he is designated to succeed, but no constitutional or statutory provision prohibiting a legislator from holding another office or prohibiting the holder of another office from being a legislator shall be applicable to an emergency interim successor. An emergency interim successor shall serve at the pleasure of the legislator designating him or of any subsequent incumbent of the legislative office.