Oh I thought you were looking for ways to get a king. Nevemrind
There is the coup option led by the military. During the latter days of the Roman Empire, a general was playing hide the sausage with his wife when his men rushed in and said, "We have not been paid in six months, we want to go home." The general replied, "I can do nothing, for I am loyal to the emperor." The men said to him, "Then you are our emperor, if you refuse, we will kill you and choose the next one under you as emperor." "Then I am your emperor," the general then lead the legion on attack of Rome itself - thus the Roman empire died a little more.
You could go with this option - Washington in his tent when the Continental army comes in and demands him to become King without congressional approval. Thus you have a King in America. You can do this with any military leader within American history.