I also would connect (many) codesys based PLC to Thingworx ... did you find a "smart" solution ?
I though those possible solutions
1. use codesys OPC server + gateway
2. implemente MQTT into the PLC
3. use direct REST API from the PLC
4. add a Microserver near the PLC and write to it from the PLC
5. send direct RAW data from the PLC to the TWX by using a protocol adapter in the middle
The are many possibilities with different pro and cons...