In game design you have to keep in mind, that whenever you give players more options, you are giving them more power. I don't feel this can be balanced when working from the hero-end alone.
Imagine a scale that is perfectly balanced, on one end you have the heroes(and all their tricks/abilities), on the other hand you have the villains (and all their abilities). You're trying to add a trick to one end of the scale, it's going to throw off the balance. The fact that it has some disadvantages makes it only a small trick to add, but it's still something, it's still an option. What do the villains get to restore the balance? Nothing... I'd reccomend trying to restore balance by messing with the H mechanic. Perhaps H= H+1 when using this house rule.
With that said, if your friends are losing their heroes too much, I'd say now is probably not the time to add in house-rules. When we win the game, 9.5/10 times we have 0 hero incapacitations. When we lose the game, usually all heroes are killed within a turn or two of each other. Rarely do we have one player "out" of the game on their incapacitated side for a significant amount of the game while the other heroes are still playing.
Without knowing your group I have to make guesses in wildly unfamiliar territory here, so take the following with a grain of salt. I'm guessing one of three things is happening with your group:
1. You are relatively newer players. This game does have a bit of a learning curve. It takes a while to get the hang of it. Keep plugging away and you'll learn the heroes and the villians well enough that incapacitations will stop happening.
2. You are not playing with enough players. Even though the H mechanic does help, the game is still harder with 3 players than with 4. It's harder with 4 players than with 5. If you're only playing with 3 players, add another player, or have one player play another hero.
3. Your group is playing extremely agressively. Maybe you are choosing heroes like Absolute Zero or Fanatic and bringing on the self-inflicted damage. This is fine, but you have to realize that early incapacitation is a chance you take. If incapacitation bugs them, suggest they pick different heroes or play more conservatively. You may also not be assigning much value to cards like Fortitude, Danger Sense, Synaptic Interruption, Hypersonic Assault, Throat Jab, Ground Pound, etc... things that mitigate the amout of damage you take. These are good cards, many of them are among the best in the game, don't ignore them!