RZ67 Film Back

I've googled for hours and couldn't find answer for how the RZ67 knows there is film inside it.
Does anyone know how to hack the RZ67 back and make it advance the film counter without actually advancing film?
(There is a practical reason for it)

Thanks!

I don't have one to hand but I would suspect there's a roller driven by the film, that in turn works the frame counter.

Maybe just load it with the paper backing from your last roll?

Or do you want film in it that doesn't advance? On the RB, the multi exposure lever (on the film back) does that.

A polaroid back (at least on the RB series) also lets you fire away… as does just removing the back.

I would bet that it's gear-driven off the supply spool. The takeup spool will spin infinitely and not advance the counter when there is no film in it. I think the gear drive stuff is in the bottom of the film back.

UPDATE:
thank you all for answering and a special thanks to Ian C.
Advancing the frame counter is done by advancing the black winding cylinder right under the film counter window WHILE holding down a small metal lever under the counter. In my RZ back it was hidden under the light seal foam.
If you want to advance it further after winding is 'done', use a pen to press a metal button inside a the metal part that attaches the back to the body. Otherwise, the film counter would stay at '1'.

Hope this would be helpful to someone!