Alright, so I called the German Customs today and was told the following:
When transporting goods through Germany that are destined for another country, you generally can use the "T1 Versandverfahren", with which you register your goods at the customs office upon entering Germany.
The point of the "T1" registration is that the goods are under "customs supervision" and are obviously not to be left inside Germany.
Technically, you are then transporting the goods to an Airport or Harbour or some Shipping company that should process the export for you
and you'll get proof that you have exported them again.
However, in my situation I was considering going with DHL and they might not do this or at least its not clear how the process would work right now.
Therefore, you can also announce the export yourself through a so called "Ausfuhrverfahren" using "Form 033025", which you can find on www.zoll.de
The remaining question is in which order should this happen?
The kind lady on the phone said I should immediately when importing the goods start the "T1" and launch the "Form 033025" at the same time
. It makes more sense to me, though, to first launch the "T1", then ship the goods and return to the customs officer to process the "Form 033025" for export when I can actually proof that I just shipped them.
Let me know if anyone has done this - it would be a great help!