The multiplayer commands are designed for clients to communicate with a server program. The server can be a mobile device, Mac, or PC. You could even design the client so that it functions as both. These are all designed to work over normal networks (not sure the protocol, probably TCP/IP).
There are NFC commands but the documentation says they aren't functional and if it is really NFC then they won't be feasible as the range would be way too short.
If you want to make multiplayer then I'd suggest going the TCP/IP route with the multiplayer commands or use a webserver and HTTP commands (but those might be too slow unless it is a turn based game). You'll get much better range and people can play over long distances.
You should be able to do this in tier 2. You'd need to modify the java files to have callbacks to the C++ code and set up the bluetooth in java. Gives me a headache just thinking about it
If you do go that route I imagine many folks would be interested in learning how to do it.
