My girlfriend and I tried a new way to play against weaker villains with just the two of us.
We tested it against Baron Blade in The Realm of Discord (obviously not the most difficult setup), she was Tempest, and I was Haka. To account for the "required" third hero we shuffled all the other hero character cards (from the base game, Rook City, and Infernal Relics) and placed them under Tempest's divider card. When it came time for the third hero, we pulled the top card, read the incapacitated side, and decided which ability to use. We set H=3 since there were technically 3 hero turns.
It seemed to make a more balanced game because it went 10 rounds with Tempest finishing at 13 HP and Haka at 10. The portal fiend helped out by dealing Baron 7 damage near the end of the game. Very rarely did an incapacitated hero turn seem like a waste but it also never felt like it was a game saver.
So if anyone decides to give it a try I would love to hear how it works (especially against more difficult villains).