Question: I am a Dutch citizen moving from the United Kingdom to Germany. I have received a conditional employment offer. My next employer has asked me to submit my *Lohnsteuerklasse und Steuer-Identifikationsnummer* (salary tax classification and tax identification number) at least one month prior to my start of employment. I understand that I can obtain those from *Finanzamt* (finance office), but apparently only after I have registered with the *Meldebehörde* (registration authority), for which I apparently need a *Wohnungsgeberbestätigung*. Is there any way I can get obtain the *Lohnsteuerklasse und Steuer-Identifikationsnummer* (at least) a month before my start of employment, without physically moving a month before I am due to start (which might mean being unemployed for a month)?

I suppose I would need to rent a place to get a *Wohnungsgeberbestätigung*, but signing a lease in order to register more than a month before I move without actually moving would be costly (double rent), and I fear it may be considered fraudulent, too. Similarly fraudulent may be to temporarily register at my wifes *Zweitwohnung* (secondary residence) without ever planning to live there (and the landlord may be unwilling to provide a *Wohnungsgeberbestätigung* for two for an apartment so small it is only fit for one). Is there another way out of this catch?

Answer: 
Your employer is making an unreasonable request. Either they have no idea how things are working in their country or they don't care.

The very first thing you need is an *Arbeitsvertrag*. You don't need a German tax registration or *Anmeldung* to get an *Arbeitsvertrag*.

Once you have an *Arbeitsvertrag* you can start to search for an appartment. While in theory it's not required, hardly anyone will want to show you the appartment if you have no solid job (except overpriced appartments, I speak from experience). People are not interested in short-time rental, they look for candidates with solid employment, and having a choice they will prefer those with stable employment over those with temporary jobs. 

Then, having the rental agreement, you can arrange other formalities, like tax and social security registration, opening a bank account etc.

If you have no title for German tax residency (no citizenship, no residence, no job) I doubt you'll be able to register... even if theoretically possible, it would look so suspicious, you'd most likely (once again, speaking from my experience) have big problems arranging it.
Since there are, I believe, people living in neighbouring countries and working in Germany, you should probably be able to register with the Finanzamt using your UK address.