It might not be any harder than doing it without Bitcoin. Instead of issuing a cheque in the name of the notary (potential technical troubles, high fees, etc.) or making a wire transfer (assuming notaries work that way in Germany), you will mail in the required secrets. Assuming there is a foolproof way of making it work, that is. 
That is exactly where a BTC escrow comes in. If you write a cheque you know the money is with you, and the buyer knows they have something to get to the money.
With BTC I can give you my private key but there's no knowing when you move the coins using that key and there is nothing I can do about it. Also, you might close the deal and then I move the coins myself (we both have the private key) and there's nothing you can do about it. With escrow none of us holds the private key, and we both have some recourse if something goes wrong (granted, it depends on how much one can trust the escrow). In the end, escrow service is the cheque in normal currency.
That's why I suggested multi-sig, though I think we'd need a better key exchange. My post was about figuring out a way of enabling the notary to act as an escrow without having to use a computer. Then you would go through the usual process without having to change much.
I apreciate the dialogue we have going here and all points are valid, but, could some of the champions of escrow please answer my previous questions if they so believe that escrow is a good idea. I'm just not seeing the point to it, but I fail to see how that automatically makes me a scammer, same as I also float when I go in the water and black cats do sometimes cross my shadow, but I fail to see how that makes me a witch.
I'll attempt at answering.
I've traded properties in different countries, and things wildly change from jurisdiction to jurisdiction. Once, I carried a huge chunk of money hidden in my underwear, then took it out and gave it to the seller, using a local bank manager as witness. I think exchanging property with Bitcoin is a bit like that.
If the buyer pays in advance (which I never do if I'm buying property with cash), the seller can claim that she didn't receive the money. If the seller transfers the property, there is no way of proving she didn't receive the money already.
That's where the notary comes in. I don't know how it works in Germany, but in some places (e.g. U.K.?) the notary does all sorts of research and guarantees that the property is as advertised, and can also act as an escrow for payment. If you are paying through the banking system, both the buyer and the seller can prove the transaction, so there is even less trouble.
If you can agree on a trusted escrow who is knowledgeable enough to understand the process, he would complement the notary on the BTC side of things. If there is no notary involved (change of ownership is done directly through the registry), it would be even more straightforward (though buyer then needs to investigate the property himself).