I demonstrate how to get a dual chainring working on tongsheng TSDZ2. To accomplish that I replaced the "modern" derailleur with a "vintage derailleur". The model I used was Shimano Model FD738 with 34.9 mm clamp diameter probably from the mid 90s. I believe that other vintage series from Shimano e.g. LX, Alivio or Deore will also work.

I hope this helps! If you have any suggestions or questions leave me a comment.