abarth is on the right track: "If Pprune were used as a sub-forum, it would be easy to pass the word through cockpits and have more and more guys loggin in."
It would keep strangers off the forum, and it wouldn't really matter if management learnt of the "entry-password" as long as participants could enter with their Pprune screen name(s) and maintain complete anonymity.
In the long run it would even be beneficial for management to read the posts. Managers would get first hand raw feedback from the frontline "troops!" No moderator needed on a sub-forum.
...Such as: Repetitive issues about low morale in the pilot community because of inadequate compensation; Rostering complaints; Operational shortcomings;...But also about positive suggestions on how to improve quality of life issues, safety and mutual productivity.
Curiously, most quality of life issues encompass rostering which for the most part would involve only simple, non financial remedies. In the absence of professional management and without a professional pilots organization, nobody will stick his neck out to complain about anything. So, for the time being, this is the only way to go.