With a fresh install of Besmirchment, Bewitchment and REI, and nothing else, on the latest 1.19.2 release of each, you cannot interract with Beelzebub apart from removing werepyrism by giving him garlic bread. It is impossible to enter a contract and freely control the curse.

Stare at him, judgingly, and chomp down on grotesque stew. Does not say so in the book, but that did the trick it seems.