Dragonlance?
At one point, I remember there being some kind of an alignment bar in the Dragonlance Campaign setting. You would tick off slashes for good/evil/chaotic/lawful actions. I also remember using the Bloodstone of Fistandantilus was an automatic -10 when used to drain the life and soul completely out of someone.
So what you may want to do is set something up like that and keep track in secret of the player's alignment. Let them know when to update their character sheet, and that's it. Have their actions guide their alignment.
Alignment, for me, has always been an inacurate and incomplete way of judging the moralty and personality of a character. Most characters morals go way deeper than CG/LE/LN/CG or whatever, as well as there being various shades of evil and good, law and chaos.