I have a kind of idea that Ren should re craft the helmet specifically to block out Palpatine’s whisperings. There could be a very fun connection where early in the movie, before Ren discovers Exegol, he’s communing with Vader’s helmet, and he hears these Sith whispers. After he meets Palpatine, during the Mask creation scene, he hears the whispers until they suddenly whimper out as soon as he puts on the mask. He is resisting Palpatine immediately.
I cannot for the life of me find an HD version of the TV spot that has footage of him putting on the mask, so maybe an edited shot from Force Awakens or The Last Jedi might work.
This I really like this!
Another idea could be to have Luke’s voice haunting him.