No, but there is something to keep states from subdividing their congressional districts -- the Constitution. Any system that apportions the electoral votes would have to be based either on (a) the congressional districts since electoral votes = number of congressional districts plus 2; or (b) percentage of popular vote in the state. In either case, based on recent election trends, republican candidates would syphon off more electoral votes from blue states than dems would from red states.
Well, in that post I was responding to one particularly out-there suggestion to apportion them by county.