The Strandagaldur Museum of Icelandic Sorcery & Witchcraft in Holmavik has an exhibit showcasing the macabre legend of necropants, or nábrók. According to legend, necropants could produce an endless flow of coins if done correctly. So they probably did it correctly.
To begin with, one would need to get permission from a living man to use his skin upon his death. After burial, the sorcerer would then have to dig up the body and skin it in one piece from the waist down. A coin stolen from a poor widow must then be placed in the scrotum, along with a magic sign called nábrókarstafur scrawled on paper. Once worn, the scrotum of the necropants would never empty of coins so long as the original coin remains.
For more on necropants and other bizarre occult traditions of Iceland, check out the museum’s website.