As came up on another thread (or earlier in this one?), I think the idea of an XP adjustment for conforming to character class function - which is what the PHB intimates - actually makes more sense, though whether 4 scales are needed is up for grab! You could do it in three steps: didn't conform to alignment or character class function = 2, did one or the other = 1, did both = 0. This could even be done Burning Wheel or Torchbearer style: Did you take an action that significantly violated your alignment? Gain one point. Did you engage in actions during play that significantly departed from class function? Gain one point. Each point is (say) a 15% penalty to earned experience for that session/adventure.