I am not very good at story writing, if anybody is willing here is the plot:
A priest of Cybele normaly needs to cut off his balls at the festival for her sake. Normally, the priest lives in the temple before the festival and gets ready for the big event. This time our priest decides to master castration and not bleed to death. Steals money from the givings for the Godess and buys slaves, that match his own balls, and starts to simulate his own castration on the slaves. Standing behind them and practicing every movement with both hands, holding an cutting off the pair.
The task is not easy he needs to be totally nude he should find a method that will ensure he is still alive after the cut.
A solution might be being biten by the balls by a snake:
https://www.youtube.com/watch?v=4WvnjCkLbvY
The end of the story is upto the writer, maybe he will decide to save one of his balls after the scrotum is cut.
If you like the plot I am sure one of the greatest writers might want to create a good story out of this.