Combine first 5 ingredients in a medium bowl; cut in margarine with a pastry blender until mixture resembles coarse meal. Add buttermilk, stirring just until dry ingredients are moistened.
Sprinkle 1 1/2 teaspoons flour evenly over work surface. Turn dough out onto floured surface, and knead 5 or 6 times. Roll dough to 1/2-inch thickness; cut into rounds with a 2 1/2-inch biscuit cutter. Place rounds on a baking sheet coated with cooking spray. Bake at 425° for 10 to 12 minutes or until biscuits are golden.