Hmm, Not really sure. If you do this at the end node/sensor side, it will send it to the coordinator if you do not know the address: XBeeAddress64 addr64 = XBeeAddress64(0x00000000, 0x00000000);
I am assuming you can create a new instance on XbeeAddress64.
Here is how I parse the MSB and LSB of the Address64 at the coordinator side when a sensor posts/sends data into a string:
String iDnodeMsb = String(rx.getRemoteAddress64().getMsb(), HEX);
String iDnodeLsb = String(rx.getRemoteAddress64().getLsb(), HEX);
String iDnode;