I fixed it with installing the GeDoSaTo executable from http://blog.metaclassofnil.com/?page_id=582 (where it says "Finally, download this executable [...]") to my E: drive where also all my Steam games are located. After that I started the NMM, selected Dark Souls 2 and entered the directory of the GeDoSaTo installation into the third input field (which is empty in the picture above).