Wrap garlic in foil. Place garlic and corn on a jelly-roll pan coated with cooking spray. Sprinkle 1/4 teaspoon salt over corn. Bake at 425° for 15 minutes, stirring every 5 minutes. Unwrap garlic, and mince. Combine garlic, corn, broth, water, 1/4 teaspoon salt, and pepper in a medium saucepan. Bring to a boil; gradually stir in couscous. Remove from heat; cover and let stand 5 minutes. Fluff with a fork; stir in onions and pimento.