I don't know about a dummy N9 but I bought a dummy N900 once to see what it was all about.

It looked superficially very much like the real thing, except of course there was no display, only a piece of printed paper. But that was expected. The keyboard slider worked just like the real one. There was no real keyboard but that was expected too.

Unfortunately, on closer inspection, everything was different. Nothing was reusable for spare parts, not even the screws.