How does praiseworthy convince the justice of the peace not to hang cut eye Higgins in by the great horn spoon?

In the novel "By the Great Horn Spoon!", Praiseworthy convinces the Justice of the Peace not to hang Cut Eye Higgins by presenting a false letter from President Polk, claiming that he needs Cut Eye's services on a top-secret mission. This lie convinces the Justice of the Peace to release Cut Eye into Praiseworthy's custody.