Put this in the server console:
$Pref::Server::BrickCount=-1;
Then, you need to post to the master server.
Easiest way to do that is just type this in your chat:
/timescale 1
Yes, changing the timescale posts to the master server.
Edit:
You can also edit the number of players in the server with something similar.
Not the max players, but the number of current players. ;)
Can't just say what it is or noobs will use it to try to get more people.
If you have a brain though, you should be able to guess it easily.