We had the same problem with files added to the vault. For these files in workflow I created an intermediary state and an automate transition. In this transition I cleared any variable value that is inappropriate for just added files.
For values that will only be read from CAD files like mass etc. I made those variables read only in cards and I unchecked default value in card editor. In this case PDM read variable values from CAD files.
We are ending up doing a similar thing. It is annoying that you have to version the file just to set the variable to what it should be in the first place.
I guess this is a decent work-around for the mean time.