Just an idle thought for a BBC or BNWO fantasy: Some sort of implant that stimulates the cuck's prostate on command. Could be used like clicker training, give the prostate a pulse every time the cuck performs a task for his wife or master, or every time he is humiliated, or every time his wife cums on a black cock. No brainwashing or anything like that required, the cuck is just gradually forced to associate that intense helpless pleasure every time the BBC master gets what he wants until the cuck learns to actively seek that pleasure out. As a special treat, maybe he gets to be tied to a chair in his bedroom with the implant running full power as the BBC master rails his wife in front of him, helpless to do anything but moan as his tiny white dick dribbles his useless seed onto the floor.