So i bought myself a new Clip Sport and found out, that resume on an audiobook with many files is not possible…
I looked in my own blog about the workaround for the Fuze+ and did the mp3wrap thing on linux with an audiobook. After that i set the correct tags and this i think works for me. With the Fuze+ i had to re-encode the wrapped file, with the sport this seems not to be necessary.