A few thoughts:
RN and RM Warrant Officers up until 1949 were classified as Officers and were saluted. They were appointed by Warrant and had their own WOs messes. There were also Chief Warrant Officers who held commissions. In 1949, the RN and RM WOs were all commissioned as 'Branch Officers' and became members of the Officers Mess/ Wardroom. The Branch Officer rank was abolished in 1957.
And the Gurkha Regiments in the British Army have officers who rank between a British WO1 and 2nd Lieutenant. These are the Queens Gurkha Officers (QGOs)
So it shouldn't be too difficult for those in the corridors of power to communicate the official policy on how to treat US Warrant Officers.