As far I my understanding goes, you don't need to fiddle with any such setting on the Mac client. It essentially always runs in an internet connection lurk mode, so to speak. Thus, if it is installed on a computer with an always on connection, the client effectively runs in "online always" mode. Similarly,
if it is installed on a system with dialup access, the client effectively runs in "lurk" mode.
So in short, just install the client and you should be fine. Hope this helps.