The OMNI Flow uses the Enron Modbus protocol and the HPM interface of the TDC does not support Enron Modbus. You will need to bridge the data between Enron Modbus and regular Modbus to get the communications established. You can use Kepware's KEPServerEX and Modbus Driver suite with LinkMaster to do the bridging. For Details contact Kepware Technical Support or Kepware Sales.
I work for a company called HMS and we manufacture, among other things, gateways. We have a gateway that can be configured to poll one register and handle the 32 bit response. On one side of the gateway, it will act as a standard Modbus RTU slave device and the other side can be programmed.