As noted, the Germans could move their factories beyond the range of escorted bombing missions, which would not become possible on a strategic scale until 1947 with the introduction of the F-82 in large numbers; first flight of that wasn't achieved until October of 1945, so I don't see much acceleration being possible of the same. Likewise, the B-29 is no answer, given that it's maximum altitude is matched by the maximum range of contemporary German AA guns. U.S. leaders were also well aware of this, as
Leslie Groves revealed when interviewed on the subject of atomic weapons on Germany:
REPORTER: General Groves, could we go back for a minute. You mentioned in your book [Now it Can Be Told] that just before the Yalta Conference that President Roosevelt said if we had bombs before the European war was over he would like to drop them on Germany. Would you discuss this?
GROVES: At the conference that Secretary Stimson and myself had with President Roosevelt shortly before his departure, I believe it was December 30th or 31st of 1944, President Roosevelt was quite disturbed over the Battle of the Bulge and he asked me at that time whether I could bomb Germany as well as Japan. The plan had always been to bomb Japan because we thought the war in Germany was pretty apt to be over in the first place and in the second place the Japanese building construction was much more easily damaged by a bomb of this character than that in Germany. I urged President Roosevelt that it would be very difficult for various reasons.
The main one was that the Germans had quite strong aerial defense. They made a practice, as every nation does, that when a new plane came into the combat area, that they would run any risk that they could to bring such a plane down so that they could examine it and see what new ideas had come in so that they could make improvements and also would know the characteristics of the plane so that they could prepare a better defense against it. We had no B-29’s in Europe. If we had sent over a small squadron or group as we did against Japan of this type, everyone of them would have been brought down on the first trip to Germany. If they hadn’t been, it would have been through no lack of effort on the part of the Germans.
The alternative would be to bring a large number of B-29’s over to to England and that would have been a major logistical task and the other possibility would have been to have used a British plane which would not have been a bit pleasing to General Arnold and also would have created a great many difficulties for our general operation because then it would be an Allied operation with the United States furnishing the bombs and everything connected with it but using a British plane and a British crew to actually drop the bomb and it would have raised a tremendous number of difficulties.
And difficulties like that — while you say you should be able to handle that — you can but in a project of this character there are so many little things, each one of them key, that you can’t afford to throw any more sand into the wheels that you can help.
The bombing of Germany with atomic bombs was, I would say, never seriously considered to the extent of making definite plans but on this occasion I told the President, Mr. Roosevelt, why it would be very unfortunate from my standpoint, I added that of course if the President — if the war demanded it and the President so desired, we would bomb Germany and I was so certain personally that the war in Europe would be over before we would be ready that you might say I didn’t give it too much consideration.