Contraband oil shipped or transported in interstate commerce in violation of the provisions of this chapter shall be liable to be proceeded against in any district court of the United States within the jurisdiction of which the same may be found, and seized for forfeiture to the United States by a process of libel for condemnation; but in any such case the court may in its discretion, and under such terms and conditions as it shall prescribe, order the return of such contraband oil to the owner thereof where undue hardship would result from such forfeiture. The proceedings in such cases shall conform as nearly as may be to proceedings in rem in admiralty, except that either party may demand a trial by jury of any issue of fact joined in any such case, and all such proceedings shall be at the suit of and in the name of the United States. Contraband oil forfeited to the United States as provided in this section shall be used or disposed of pursuant to such rules and regulations as the President shall prescribe.