The best thing is to simply raise the car up. Use an old book or something else. B/c not only are you concerned w/ the springs, but you need to protect the tires.
If you are storing your car for a period of time, the foam in the tires can actually start to become compressed and the bottom part (sitting on the ground) can remain flattened out.
This will definitely throw you tires out of balance the next time you drive it. Circles tires roll better than square ones (not being a smartass).
Later....