Season the squash with 1 tablespoon of the oil, salt and pepper. Place on a baking sheet and roast for 45 minutes to 1 hour or until tender. Remove from the oven and cool completely. In a blender or food processor, puree the squash with 2 cups of the chicken stock. Puree until smooth and set aside.
In a saucepan, over medium heat, bring 4 cups of the stock and 1/2 cup of the chopped onions to a simmer. Stir in the rice and cook until the rice is tender and the liquid is absorbed, about 1 hour, stirring occasionally with a fork. Remove the rice from the pan and cool. In a large saucepan, over medium heat, add the remaining tablespoon of oil. When the oil is hot, add the sausage and brown for 3 minutes. Add the remaining 2 cups of onions and corn. Season with salt and pepper. Saute for 3 minutes. Add the remaining 6 cups of stock and squash puree. Bring to a boil. Reduce the heat to medium-low, cover and simmer for 20 minutes. Skim off any fat that rises to the surface. Stir in the rice and continue to cook for 10 minutes. Remove from the heat, stir in the half-and-half and reason with salt and pepper. Stir in the parsley and serve.