I sent SoundTraxx an email and told them I would buy 10-15 Blunami decoders if they added a chuff input or output.
Sans a reason why it wouldn't be easy, with 20+ years of software development experience myself, including 10 doing embedded systems programming, I tend to agree with John.
My guess is that they are shy to do it because of the litigious nature of the other 3-rail manufacturers.