Are you talking about zone enumeration? That's covered in the article.
(I'm not sure if this is what was being asked, but I'm curious about the answer to that, either way.)
(Phreebird is an online signer, but I don't see why an offline signer couldn't generate these proofs.)
If there is any company in the world actually using Phreebird in production, I'd --- for more than one reason --- like to know about it.
(And indeed, it cannot be done offline - although doing much narrower NSEC/NSEC3 ranges than 'normal' could be done offline).