The first one is pretty easy. Just have the 1968 election end with a hung college. The total clusterfuck that would follow would convince the US to reform the EC and this is pretty easy to do considering how close the election was. Just look at Fear, Loathing, and Gumbo to see the total chaos resulting from a hung EC.
The second one is far harder. Perhaps the Democrats gerrymander the districts so horribly while they were in power the Republicans begin winning decisive majorities but Congress is still Democratic-controlled?
1. That would work. I can imagine the spectre of George Wallace going a great way in convincing both Democrats and Republicans to form the Electoral College.
Maybe if Nixon makes an extra gaffe or two, then Wallace narrowly wins an extra state and Humphrey takes some of the closer states, and there's a hung EC . . . oh my.
Y'know, I might look to collab with someone on a TL where this takes place and leads to electoral reform.
2. Also, a good idea. I could imagine one party gerrymandering the districts to hell, winning the majority of seats yet the minority of votes a few times in a row, and after the other party comes to power, they start reforming the system.
Here's how. Louisiana style primaries. Top 2 candidates from opposing parties then go on to the general election.
The popular vote also counts as 10 electoral votes.
In case of an electoral tie, the electoral votes are then calculated by congressional district, minus DC's districts (535).
This Louisiana system is actually similar to how the president of France is elected, by two-round runoff voting.