Funds available under this chapter may be used to pay costs of training employees employed or assigned pursuant to section
2506
(a)(2) of this title (through interchange or otherwise) at any State or local unit of government, public or private nonprofit institution, trade, labor, agricultural, or scientific association or organization, or commercial firm; and the provisions of subchapter
VI of chapter
33 of title
5 may be used to carry out the foregoing authority notwithstanding that interchange of personnel may not be involved or that the training may not take place at the institutions specified in that Act. Any payments or contributions in connection therewith may, as deemed appropriate by the head of the agency of the United States Government authorizing such training, be made by private or public sources and be accepted by any trainee, or may be accepted by and credited to the current applicable appropriation of such agency: Provided, however, That any such payments to an employee in the nature of compensation shall be in lieu, or in reduction, of compensation received from the United States Government.