He can't. He's American. The United States is not a British Realm nor does the Queen reign there in any singular separate fashion as she does in Australia as Queen of Australia and likewise NZ and Canada and other realms.
Honorary Knighthoods are bestowed upon US and other foreign citizens from time. Bill Gates, Michael Bloomberg and Alan Greenspan for instance have all been knighted as Knights Commander of the Order of the British Empire( KBE) as was the great Austrian pianist Alfred Brendel.
Why Meatloaf has not been bestowed an honorary knighthood can only be speculated upon. Maybe the name LOL... not sufficient gravitas perhaps.
