I'm not from Germany, but I have the same doubts about it.
For the moment I opted for just not collecting the money, as any other path would cost more money that what I would potentially earn in 1 year.
And there's no "free" way to pay taxes in my country for sporadic sales, as the one's I receive. You'll have to pay a base fee on a monthly bases whether or not you've earn something.
Anyways, I'd like to read what others have to say about this