He would have to convince his fifteen colleagues to make this a Germany-wide thing. Handling this on the federal level is not even possible in Germany, the federal data protection appointee has nothing to say about such matters.
It would only take someone to go to their local data protection supervisor (Datenschutzbeauftragten) and complain about being tracked by the facebook like button on a site hosted in germany, the data protection supervisor would have to issue a fine (if he agrees with that interpretation of the law) and it would go to court, since the owner of the website would naturally dispute it.
Difficult to say how the court would rule.
The laws are not (only) enforced by the police but by specialized offices – just like tax law (with the tax office and tax investigators) or food law (with food inspectors).
This is like the police (which is organized in a similar way) in Bavaria deciding to enforce a federal law in a certain way. Whatever the police in Bavaria decides to do doesn’t have to have any consequences for the police in other states. (Suffice it to say, the police in other states isn’t going to be very happy when they hear about the Bavarian police interpreting a law in an odd way.)
It’s the courts that have to decide in the end what is correct and incorrect enforcement.