Electors are people, my friend.
To allow for a fractional proportional method, would need a constitutional amendment to abolish the Electoral College, and could be stopped by states with as little as 3% of the U.S. population.
Without an amendment, the office of presidential elector remains. A presidential elector is a person, and a person’s vote cannot be divided into fractions. Each state would have to use a whole-number proportional approach.
States can assign electors any way they wish.