Dissolve yeast in warm water in a large bowl; let stand 5 minutes. Lightly spoon rye flour into dry measuring cups; level with a knife. Add rye flour and molasses to yeast mixture, and stir until combined. Cover and let stand at room temperature for 8 hours or overnight to make a sponge.
Stir oil and salt into sponge. Lightly spoon whole wheat flour and bread flour into dry measuring cups; level with a knife. Add whole wheat flour and 1 1/2 cups bread flour to sponge; stir until a soft dough forms. Turn the dough out onto a lightly floured surface. Knead until smooth and elastic (about 8 minutes); add enough of remaining bread flour, 1 tablespoon at a time, to prevent dough from sticking to hands (dough will feel tacky).
Place dough 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 size. (Press two fingers into dough. If indentation remains, the dough has risen enough.) Punch dough down; cover and let rest 5 minutes. Divide dough into 2 equal portions. Shape each portion into a (6-inch) round. Place dough rounds on a baking sheet sprinkled with 2 teaspoons cornmeal. Lightly coat surface of dough with cooking spray. Cover and let rise in a warm place (85°), free from drafts, 20 minutes or until doubled in size.
Preheat oven to 350°.
Uncover loaves. Place 2 tablespoons bread flour in a small sifter, and sift flour evenly over loaves. Cut a shallow (1/4-inch) X in the center of each loaf. Bake at 350° for 1 hour or until bread is browned on bottom and sounds hollow when tapped. Cool on wire rack.