yeah taking the freighter is a nice way to go....keep in mind though they will typically get in at night, and most likely no trains available to Berlin so you will have to spend the night in Leipzig or Halle. On the way back however, the flight will leave in the evening so easy to take the train. Will get in to CVG at nite, but could jump on a DHL flight to wherever home is.
I think maybe once a week there will be flight getting in during the day, so if possible use that.
good luck