Without a constitutional amendment, there is no way to compel states to award their electoral votes proportionately.  I'm not sure why you would want to retain the EC if you think it should just be pro forma.  If we're going to amend the constitution, I would rather just allow the popular vote to determine the election.  If we aren't able to amend the constitution, there is a movement called the National Popular Vote initiative that states can join that says that the state will give all it's electors to the winner of the national popular vote.