Is it possible to Export in Grayscale mode png-8

[i73]

By default when exporting png's it will be PNG8 indexed (With color information) for us to get true Grayscale artists have to turn on the Grayscale mode:

Can I export each layer with the proper png8 Grayscale, without having to select Grayscale mode?

[i73]

Now I see I can use:

  error = sPSActionDescriptor->PutObject(desc, keyAs, classGrayscaleMode, EPSDescriptor);

  if (error) goto returnError;

     ...

  error = sPSActionControl->Play(&result, eventExport, desc, plugInDialogSilent);

  if (error) goto returnError;

But that's just breaking my action when I add it. Any suggestions?