Combine first 3 ingredients in a 1-cup liquid measuring cup; let stand 5 minutes.
Combine yeast mixture, 2 cups bread flour, rye flour, cornmeal, and salt in a large mixing bowl; beat at medium speed of an electric mixer until ingredients are well blended. Add yogurt, margarine, and 1 1/2 teaspoons caraway seeds; mix well. Gradually stir in enough of remaining 1/2 cup bread flour to make a soft dough.
Sprinkle 1 tablespoon bread flour evenly over work surface. Turn dough out onto floured surface, and knead until smooth and elastic (about 8 minutes). Place in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, 1 hour or until doubled in bulk.
Punch dough down, and divide into 16 equal portions; shape each portion into a 16-inch rope. Place on baking sheets coated with cooking spray.
Cover and let rise in a warm place, free from drafts, 15 minutes or until puffy. Combine egg white and 1 tablespoon water; brush breadsticks evenly with mixture. Sprinkle evenly with 1 teaspoon caraway seeds. Bake at 400° for 17 to 20 minutes or until golden.