Hi there!
I apologize! I mis-typed when I put in weimarstudies. You can absolutely point "blog.jochenhung.de" and point it towards "jochenhung.wordpress.com."
There is no way for you to create a CNAME for just the route of "jochenhung.de" and have all traffic come here. The root of your domain (the @ record) requires that it be an IP address, which we do not provide. So you could only point the "www", and the way our systems are set up would cause errors if you tried it that way.
Your final suggestion, to close your account with hosteurope and transfer your domains, you are welcome to do, however you will need to transfer them to a different company than WordPress.com. We are unable to accept domain transfers. There are however a vast array of companies which work wonderfully as domain registrars which you may want to consider.
This article is a little old, but here is an independent article on the five best domain name registrars which you might want to consider:
http://lifehacker.com/5683682/five-best-domain-name-registrars