Yeek in the Halfling Ruins: If your willpower is not >=10+2*(lvl of dungeon), rage is the only dialogue option with the yeek. Otherwise, it is added to the menu. If chosen, it gives -2 Willpower permanently. If you kill the Yeek, you get something like permanent +20% mind penetration. (Or maybe allow training of fateful aura?)
Lumber jacks: As a cursed, you shouldn't be able to swap with the lumberjacks. Because of the design of that level, that would mean slaughtering your way through them, to reach the Cursed who's slaughtering them. I think that's a good way for Cursed to deal with the situation.
Escort Quests: Difficult to balance. Same option/mandatory effect from willpower as with the Yeek. If you strike them down, you lose 2 willpower permanently, and gain the choice of the magic or antimagic options. (With the exception of the temporal explorer: I would recommend giving something like permanent 10% temporal resistance upon striking down your future self

Merchant: Again, slightly difficult to balance. Same willpower requirements to choose to spare him, same willpower cost when giving in to your rage. If you give in to your rage, you now receive something like 0.5*sqrt(gold) bonus to max hate.
Hidden compound slaves: Even after you kill their controller, keep the slaves red (although not hostile), so you have to slaughter your way through them, rather than being some kind of savior.
Hidden compound arena master: Same requirements, same WP cost. Gives you the ring and +4 mental saves when you slaughter him.
Melinda: Same requirements, same -2 willpower if giving in to your hate. If you strike her down, get +4 spell saves. If you don't, I would personally prefer that she reject you when you hit on her. (but still give you the ring). Making a happy little family with Melinda is the least Cursed-like thing in the game.
Aeryn: Just can't imagine it working with her without breaking the rest of the game. Not a big deal, since she isn't doing provocatively whining, "Save me!"
I think that should handle the wrong-ish situations that come up, without breaking any questing, and do so in a flavorful way.
Not totally sure about these benefits-- some of them may be a little out of whack-- but I think without benefits, and without ever being forced to, Cursed players will just choose the min-max, good guy option all of the time. One thing I like about this proposal is how giving in to your rage is a sort of positive feedback loop, with you becoming increasingly incapable of choosing not to once you start indulging. (I would like to see all NPCs treated as red bordered enemies, but I can't imagine that working well in the towns.)