The Secretary of the Senate is hereafter authorized to advance, in his discretion, to any designated employee under his jurisdiction, such sums as may be necessary, not exceeding $1,500, to defray official travel expenses in assisting the Secretary in carrying out his duties under the Federal Election Campaign Act of 1971 [52 U.S.C. 30101 et seq.]. Any such employee shall, as soon as practicable, furnish to the Secretary a detailed voucher for such expenses incurred and make settlement with respect to any amount so advanced.