IME, saddle rails aren't strong enough for truly frozen posts. If you can get it out by twisting a saddle, given the amount of leverage offered, I think it barely qualifies to be called a frozen post.

If you don't have a vise, a large pipe wrench on the post, just above the frame is the next best choice. However, whether you use a vise and turn the frame, or use a pipe wrench on the post, you'll have enough torque available to twist the frame, so use some judgement regarding how hard you twist that puppy.