"This variant could be interesting in a public press game where only "grey" message were allowed. "
@Bozo, excellent observation. This kind of variant is extremely fun. A few years back I played in and GM'd a couple of games on the Imperial map that offered *only* public press, with the options for white, grey, and black press. With the right roster of players it can be a roller coaster.
To summarize the concept, all press was public. In the games I played, this meant sending it via email to the GM, who collected and posted it at scheduled intervals. I'm not sure if the game options support this, but it could be handled in a forum by linking the game (created as anonymous) in each post. Therefore you create the game as gunboat - no press, and then handle press through the forum with strict rules that ALL press most be anonymous (which is accomplished by linking the game in your post).
White Press: a message written by a player playing a nation (Austria), representing that nation (Austria).
Grey Press: A message written by a player claiming no identity of nation at all
Black Press: A message written by a player (Austria) posing as another nation (England).
All press is public and anonymous, so it's a war of wits to decipher who is real, and who is Memorex.