Another alternative is to simply insist that "non-votes" be given the same weight as votes cast. That way candidates would have to inspire sufficient voter to get off the couch for the winner to gain an actual 50%+1 of the ELIGIBLE voters.
People who don't vote aren't saying "whoever wins the horserace can do what he/she likes". They are saying NONE of the "viable" candidates are worth the effort of voting for, and that includes the splinter candidates.
If the splinter candidates/parties were THAT much better, different than the duopoly, they'd get more votes. But because they are often selling single-issue or extreme-position politics, John and Jane Q. Public can't identify with them, nor be motivated to "make a difference".
It doesn't help that the duopoly uses the state police/spy/media to limit public awareness of, or access to, alternatives.
If voting, particularly for non-Dem/Rep candidates is to have an effect, and because the internet is now unsafe for significant organizing, the time has come to be knock on our neighbours' doors outside the election propaganda cycle. The public needs to see that true pan-issue progressive activists live where they do, and are not just there to grab votes, then disappear for 4 years.