If your floor is not level, more contact area may just make rocking worse.  For example, in Hairy's solution above, if there is a high point in the middle of the 4x4, the saw may teeter; however, with adjustable feet at the corners, you can adjust each corner independently and completely eliminate rocking.  

--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.