You can't find or buy the game in the German store, but activating the key is not an issue. That's what I did with Paradise Lust. I was very happy to see that you also get a Steam key when you buy the game here and wish more developers would handle it like this. The censorship on the German Steam store really is a pain in the ass.
@sonkhawk You can hide the game in your library, or simply create a second Steam account to be safe.