Looking for a magic ring-gag story

I read a story years ago that I have been unable to find. It was about a man who goes to a magic shop, possibly Spells R US I don’t remember and buys a ring gag that transforms his reluctant girlfriend’s mouth into an undulating mass made for deepthroating. Anytime he says a magic word her mouth transforms and she is immediately drawn to him to give him a blowjob. Does anyone know where I might find this story? I’ve searched SOOOO much, but can’t find it.