At any time after the approval of an agreement or after the entry of the award, a sum equal to all future instalments of compensation may (where death or the nature of the disability renders the amount of future payments certain), with the approval of the board, be paid by the employer to any savings bank, trust company, or life insurance company, in good standing and authorized to do business in this Commonwealth, and such sum, together with all interest thereon, shall thereafter be held in trust for the employe or the dependents of the employe, who shall have no further recourse against the employer. The payment of such sum by the employer, evidenced by the receipt of the trustee noted upon the prothonotary's docket, shall operate as a satisfaction of said award as to the employer. Payments from said fund shall be made by the trustee in the same amounts and at the same periods as are herein required of the employer, until said fund and interest shall be exhausted. In the appointment of the trustee preference shall be given, in the discretion of the board, to the choice of the employe or the dependents of the deceased employe. Should, however, there remain any unexpended balance of any fund after the payment of all sums due under this act, such balance shall be repaid to the employer who made the original payment, or to his legal representatives.