The fake will included the LDS church so that they would feel the need to do something with this document on their desk. If it were just a nuisance, they might have tossed it in the fire, but it gave them a piece of the pie.
To complete this analogy, the Roman Catholic Church had several "Gospels" on their desk and they tossed any that they felt did not give them the biggest pieces of the pie. You see, all of them were fakes, so they didn't want to have competing fakes all over the place. They selected 4 gospels to survive and attempted to toss all remnants of any others.
The analogy is not perfect because these fake gospels were not only on their desk but were out there in the community. Their selection would have been tighter were that not the case.
The biggest difference here is that, although Hughes never wrote the Dummar will anymore than Jesus wrote a gospel, Hughes was real and could have met Dummar and the fortune mentioned in the fake will was real.