It's pretty obvious that he used the elf equivalent of apparation, but are we ever actually told that?

Ever since the scene in Goblet of Fire where Crouch's means of disappearance are discussed, I've been finding more and more loopholes in the excuses based around not being able to apparate in Hogwarts. I'm looking to see if we knew anything about how Dobby cheated that rule back in the second book.