In my explorations, the first person to actually use the term pious fraud in conjunction with Mormonism was Mark Twain in Roughing It. Surprisingly, the reference was not to Joseph Smith, but to Brigham Young allegedly dressing up as Joseph Smith. This is Twain’s take on the narratives about assuming the prophetic mantle. More recently, Dan Vogel’s biography is essentially a book length defense of an earlier 1996 essay championing the pious fraud model as the most plausible solution framed by Jan Shipps in “The Prophet Puzzle:”
What we have in Mormon historiography is two Josephs: the one who started out digging for money and when he was unsuccessful, turned to propheteering, and the one who had visions and dreamed dreams, restored the church, and revealed the will of the Lord to a sinful world.