In the spirit of "dangling the carrot" I suggest incorporating a mechanic from an other game system. There is a little indie RPG called "Fate" which actually awards characters for good role playing. What you do is you have your characters write up a list of "aspects". These are simply words or phrases that say something about your character, such as "drinks like a fish" or "Death before dishonor!" Any time a character plays to their aspects you can award them with a "Fate Point" (use some kind of counter, like game tokens, pennies, ext.). These Fate Points can be used by the players to shift the game in their favor in a couple of ways.
They could spend a point to improve a role by two points, or re-role a bad damage role. More interestingly, they could use a point to make a "declaration" about the game world. For example, being chased through the streets of a busy city the player could declare that a merchant pushing a cart of vegetables conveniently cuts off their pursuers, thus giving the player more of a lead. The GM, of course, has absolute veto power, but so long as the declaration is reasonable, isn't game breaking (like having an adversary suddenly drop dead from a heart attack) and doesn't present any continuity issues, then let it fly.
An other interesting part of aspects is the freedom to "compel" them. Let's say somebody is playing a thief with the "cowardly" aspect, when they suddenly decide they are going to jump into the fray and face off with some horrifying beast. This is rather out of character for them, so what you can do is compel them with tantalizing Fate Points!
"My cowardly thief lunges at the terrifying aberration and stabs it with his puny dagger!" asserts the player. "Does he?" enquirers the GM as he slides a Fate Token across the table. "Those spiked tentacles look awfully nasty." The player then has the choice to accept the fate token and give in to his cowardice, or they can resist the compulsion by meeting the GMs wager with a Fate Point of their own. A character can be compelled a maximum of three times per instance.
So to summarize; playing to type earns players points which can be used to improve roles and alter the game world to their liking.
Also; if racial characteristics are a big deal to you then you could make the character's race a mandatory aspect and compel it whenever you think someone is being "un-elflike" or what have you. You could also apply this to character classes and alignments. I do think, however, that any aspects that go against race or class archetypes should take precedence since these are the things that make a character unique. Also remember that characters change over time, so feel free to add, alter, and swap out aspects as the plot dictates.
Maybe you could even make Fate Points exchangeable for XP. The whole idea is that this gives you a means of directing play but not without giving players new freedoms in return.
