the weight distro of the S is 50/50. ditto the Miata (own/driven both in snow). IME, adding extreme amounts of weight to the rear is NOT a good thing for either car (yes, tossing sand to the ground is great for traction when you're stuck, but salt would be even more practical in that instance).

once the car even begins to move, the weight is transferred to the rear... a good set of snow tires is > any weight in sand/bricks.