Apart from changing the electronics, you do have some options but all require some additional items.
1. If the PLC/DCS can read HART variables, then you can use HART, taking mass flow as the PV and the temperature readings as the SV.
2. Use a HART divider, such as the Moore HIM, which takes the Hart signal and provides additional 4-20mA from that.
http://www.miinet.com/?page=product&cid=hart-gateways-monitors-and-int&id=HIM_HART_3AO_24DC_DIN_hart
3. Use the frequency output directly to the control room, scaled e.g. 0-1000 Hz = 0 – 200degC.
4. Use the frequency output and pass through a D-A converter to change Frequency to Current.