The Germans won't be able to tip ICBMs with nuclear warheads because they won't have any nuclear devices.
As to tipping 3 or 4 ICBMs with B or C warheads by early 1945, there is a very faint possibility of that. At a time when an Allied crop-duster can overfly most of Germany, it wouldn't be such a good idea, though.
I said maybe they will have nukes. Besides, a dirty bomb could also do the trick. Imagine an ICBM striking NYC, frightening lots of Americans...could have caused a change in policy.