I think you need to think of someone other than the US for Germany to attack. They could do a night raid on the UK, bombers were still attacking in ones and twos, or a V1 launch from a H111 or such like they did normally at this time period.
The problem with hitting the UK is that they would hit back hard, really hard. Anthrax is something they have in their arsenal and IIRC intended to use if they got hit with chemical weapons.