I hope I didn't misunderstand your question. If so, please let me know, and ignore the following paragraph.
Please note that enabling backface culling of a Spine skeleton does not make a lot of sense, be it on the runtime side or in the Spine Editor. This is because any negative scale of attachments (for flipping them from left to right, etc) would lead to the winding order changing from CCW to CW and vice versa, turning a front- into a backface. You would want to render all attachments however, not only right-facing ones, so culling mode should then be set to None as a consequence.
