This is actually the way a number of states organized their state legislatures until the practice was barred by the Supreme Court in the 1960s in Baker v. Carr and Reynolds v Sims under the "one man one vote" doctrine.
Ah, thanks for bringing that up, I know of the cases but couldn't remember the names; but yeah, this is pretty solid SCOTUS case law for why the OPer's suggestion is unconstitutional.
Unconstitutional, that is, unless you have either (a.) an amendment allowing for explicit gross malaportionment in CD size, or (b.) had a (complimetary?) constitutional amendment which mandated that every county in America was the same size, population wise.
(a.) Is pretty unviable, even by the standards of, say, Antebellum census politics, and certainly wouldn't survive into the modern era, while (b.) sounds more plausible in democratic theory, but would be a nightmare to implement.
Dear God, NO! If you think gerrymandering is bad now, imagine how much worse it would be if they were used in presidential elections.
Well, if every state went down the path of clean, nonpartisan boundary drawing it wouldn't be so bad, but that's a helluva a condition to get in the first place.
My idea remains: have every state divide it's population into cleanly drawn, non-congressional-seat-related electoral college districts (say, by each quarter million of the pop, something like that) and award each district in the standard US method, while the winner of the overall vote in the state gets a top-up of two delegates.