Sometimes this just takes the right players, Or training/Retraining the players to play differently.
Sometimes this takes a Carrot. In another Game system I run, They have a Game mechanic Called Honor. It can be used much like Fate points are In RM, to save your character when catastrophe strikes the dice. But the name is misleading.
Honor in this game is more like Dharma or Karma. The Players can earn or Lose points of Honor each level Based on 4 categories Judged by the GM.
#1 Playing your Class. This isn't necessarily Playing the Stereotype of your class (i.e. All fighters must be brutes wielding swords and charging in to beat down the enemy) But if your a Fighter and you cut and Run leaving the Mage and the Thief to Fight off the baddies every time a Combat does ensue, well maybe you should have chosen another Professions.
The Way I personally Judge this is to Talk to the player about their character concept when they are creating the character so I have an Idea what "they" intend their character to be. Then I judge based on whether they live up to their words.
#2 Play your alignment: I realize that RM was never a true alignment based system, mostly only differentiating Good and Evil, but the system this Idea comes from is a classic AD&D style game and does you the Iconic Alignment system that is Socially and Politically motivated, not necessarily Personality centric. It has it place in the Role play aspect of the game, and the players are judged based on how they live up to their chosen Alignment.
#3 Roleplaying: This one is, I think, the most important of the 4 categories. Does the player Metagame? Does he Play his characters Quirks and Flaws or try to ignore them unless the GM brings them up? Does he take advantage of information his character shouldn't have? Does he do things that are disadvantageous to himself because it would be in Character to do so? Does he Help Moderate the rules even when it is to his disadvantage to do so?
#4 is Personal Honor: This one is a bit more difficult than the others as it is more of a In Game effect. This is More character directed. And it isn't the idea of Chivalry and Honor... it is the "Respect" issue. Accomplishments that the people Hear about will increase a Characters Honor, Things they fail at or slander t their names can bring it down. Now an evil Guy may do bad things, But he would still Earn honor cause that is the thing he is KNOWN for, and may be respected/feared for such. But if some one started talking about how Gimili liked to dress up in a tut-too and dance Ballarina, And it wasn't challenged or dis-proven, or it was heard that when the Cave Troll Came out, Gimili hid in the corner and wept with fear, it would bring his honor down. Or if some guy in the bar called him Orc dung, and he didn't stand up to the guy for it, he might lose honor.... it's a GM call situation.
All of these things can raise or lower a character honor. That honor can give him in game bonuses.
Without spending any Honor, if he is in what is Called the Dishonor window, he would gain a penalty to all actions.
If in low honor he has no bonuses and no penalties.
If In average honor level he gains a bonus to 1 roll per session.
If in great honor level he gets a bonus to 1 roll per session and 1 mulligan per session. if he is in Legendary honor, he gets the last two bonuses and he gets a GM forced Mulligan per session. (he can make the GM re-roll 1 roll)
The Player Can CHOOSE to spend his Honor to Bump a Die roll or to Buy a Mulligan... but this also Lowers ones Level as you are "Cheating fate".
this is the carrot ass Players want to earn that Honor and gain those bonuses, or even just have enough points to save the butt from the fire if needed.
I currently have a Great bunch of Players who have learned that the carrot is just a side benefit and now have learned over the years that the game is So much more fun when we all play by the rules and play the characters as if they weren't Omnipotent and All knowing.