Depends on the brand of PLC. If you are lucky (running a Logix PLC), then you can use my EtherNet/IP module to pretend to be your PLC. See this topic for instructions:
If not AB, but lucky enough to be using Modbus, you can use my Advanced Modbus module's server driver to pretend to be your PLC.
If not lucky, you might be able to get the device simulator to pretend to have your OPC item paths.