If I understand correctly you have to pass the IP and PORT to the rpc call.
something like: -port=10255 -rpcport=10254
if so then you have to also put this information inside multichain.conf file so the file contents would be something like:
rpcuser=multichainrpc
rpcpassword=<your_password_here>
port=10255
rpcport=10254
I am not sure if this is what you were looking for so apologies if I am wrong here :)