How do i inject custom css for data object editing?

Situation:

  • There is a global configuration for wyswyg editors.
  • This global ckeditor configuration defines some class based styles.
  • Several data objects contain wysiwyg elements

The problem:
The wysywig editors inside the data objects don’t reflect settings for the styles.
Though the style/class is correctly applied, the text is not formatted accordingly.
For page editing everything works as expected.

The reason:
The css classes are defined in my cutom css files.
For page editing these classes can be injected using the getEditmodeCssPaths() Method
But data object editing is not editmode therefore the custom classes will not load

The question:
How do i inject cutom css for data object editing?
Using inline styles instead of the class based styles is not an option!

Thanks in advance
Jens