A piece of equipment means nothing without the correct doctrine to employ it successfully. The Germans not only had a pretty tactical, maybe opertational, mindset but they also suffered from undue meddling in military affairs and crony-ism.
A long-range bomber by itself, without long-range escorts, cannot do the job -- the Allies proved that.
Even a very long range bomber with (or without) a nuke wouldn't help -- the US is too far and too big to blanket successfully -- the Germans could not have developed sufficient aircraft or weapons to pound the US into submission before the US pounded them into submission. If you could reach the east coast, you've got a couple-three thousand miles more to get to the other side & if you can't do that, you can't win -- our industry, our training base, etc was pretty well spread out.
Now if they had nuked England (at least 2, maybe 3 hits), that might be another story, although we had bases in the Med that could have continued the long-range fight. However, England was such a hub for all troop movements, logistics, etc, etc, that her loss would have been catastrophic.
IMHO, there was nothing they could have done, once WW2 started -- it had to be something in progress/place before that -- and my vote would be not a weapon, but a strategic air force - bombers with escorts capable of covering Great Britain and deep into Russia. If nothing else, it would have made GB somewhat untenable for the buildup to a cross-channel attack. With that goes the proper doctrine and command decisions that know when to switch back and forth bewteen strategic, operational, and tactical employment.
BREAK:
Actually, I'm wrong -- what the Germans needed most was decent doctrine and SOP for use of their code devices. The Allies gained a tremendous advantage by code-breaking and radio intercepts ... It would be interesting to contemplate what it would have been like if we could not read their transmissions, even in just one area, say the U-Boat war ...
John