Given that the EC is comprised of the number of House members (435) plus the number of Senators (100) plus three for DC, it would seem best to allow EC votes to be cast as:
Popular vote in the HOUSE DISTRICT casts the vote allocated to that district.
Popular vote in the State casts the two votes allocated to state.
Three in DC cast for the winner of the popular vote in DC.
Just sayin’
With technology being what it is we may not need it.