Did you know you can use rptmidi directly from the command line in a terminal?  When used this way, the GUI (graphical user interface) is not used, and Bonjour is skipped as well.  Instead, each invocation of the rtpmidi program creates a new Session that can be a Session Listener or Session Initiator.  Working at this level you can connect if you know the hostname or IP-Address of each computer, as well as the port the RTP-MIDI session is listening on.