Dissolve yeast and sugar in warm water in a large bowl; let stand 5 minutes. Lightly spoon flour into dry measuring cups; level with knife. Add 4 cups flour, milk, sour cream, salt, and cumin to yeast mixture, and stir until blended. Turn dough out onto a lightly floured surface. Knead until smooth and elastic (about 10 minutes), and add enough of the remaining flour, 1 tablespoon at a time, to prevent dough from sticking to hands.
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 bulk. Punch dough down; cover and let rest 5 minutes. Divide dough into 3 equal portions. Working with one portion at a time (cover remaining dough to keep from drying), roll each portion into a 12 x 9-inch rectangle on a lightly floured surface. Brush each with 1 1/2 teaspoons margarine, and sprinkle with about 2 1/2 tablespoons onions. Cut each rectangle lengthwise into 6 (1 1/2-inch) strips. Stack 6 strips, coated sides up, one on top of another. Cut each stack into 8 (1 1/2-inch) sections. Place each stacked section, cut sides down, in muffin cups coated with cooking spray. Brush remaining margarine over dough. Cover and let rise for 30 minutes or until doubled in bulk.
Preheat oven to 400°.
Bake at 400° for 17 minutes or until golden brown. Serve warm.