Model changes based on weapon in hand

In the original Tribes game the model always has the same upper body position - whether he is holding a weapon or not. I would like to switch the upper body animation based on the weapon being held. To use Realm Wars as an example, the character's arm swing and body position would be different if he had no weapon, just a sword, a sword and a shield, a spear, or a crossbow.

Has anybody already worked on this and, if so, what did you find? If not, does anyone know if it would be entirely a scripting change (i.e. if (sword-in-hand) upper-body-animation = sword-run-anim;) or if I would have to alter the actual animation code to add this ability so I could access it from the scripts?

I think a scriptable solution is best so that the animation selection can be dynamically handled and tested by the modelers in game.