Well, this is a toughie...
1) The state with the best conditions for the German Jewry was probably Prussia and even they did pass several laws infringing upon Jewish rights. Maybe some small states along the Rhine and the Free Hanseatic Cities also offered good conditions for Jewish residents but I'm no expert. Also to build upon Napoleonrules's point, Napoleon did at first force the Rhinebund states to accept Jews as full citizens, but that right was abridged later during his reign.
2) Most Jews sought integration into German society, not a separation from it, as a separate "Jewish" state within Germany would've created. Also noteworthy is that German society at the time had a tendency to be very divisive: general citizenship as we know it today was only really introduced as a concept during the Rheinbund era, before that a class system was firmly in place. That would also make Jewish recognition a bit more difficult.
3) I sadly don't have accurate numbers but in the middle of the 18th century (1750-ish), there were about 70,000 Jews in Germany, with about two to three thousand living in Berlin, which probably had the highest Jewish population of any German city at the time. So overall it's pretty hard to find enough Jews to even form anything but a city state and well, city states were on the way out since the start of the Napoleonic Wars.
So yeah, I'm saying ASB unless Prussia for some reason decides to honor a noteworthy Jewish resident of theirs with a landed title and sovereignty within the new German Confederation, who then offers Jews to settle there in larger numbers. That's the only way I can see it and frankly that alone is very hard to accomplish.