I know a guy who shot a lot of rifled slugs through a full choked 12 gauge with no issues. His gun was an Ithaca 37 I believe. But that doesn't mean other shotguns would be ok. I think it is very dependent on the particular shotgun. If I talked with the shotgun manufacturer first, I would feel better about it.
I know guys who shoot 2.75" slugs in 3.5" chambered shotguns too. But I don't like the idea of a slug jumping that far before engaging the rifling. Seems like it could be dangerous to me. When I shot slugs, I always felt better matching the shell size to the chamber size. But I could be overthinking it, who knows.