[Bob]

The only logical change to the law would be to apportion electoral votes by congressional district. A presidential candidate would receive an electoral vote for each district he won and the statewide winner would receive two electoral votes representing the state’s senators.

Even that change would require a constitutional amendment. Article II, Section 1 specifies that the method for appointment of electors is to be determined by each state's legislature.

States are already free to do what you propose. I believe that there are two that do. The states can't, though, be forced to do so without an amendment.

[MediaMole]

A constitutional amendment is the proper mechanism. If a few states changed, it could radically alter the results. California and New York could hand the White House to the GOP by switching to a district by district allocation. If a few large conservative states switched, it would hand the White House to the dems.