Heat large heavy saucepan over medium-high heat and add 2 tablespoons olive oil. Reduce the heat to medium and cook the sausage until browned on both sides. Season shrimp with salt and pepper. Add seasoned shrimp and continue to cook for 2 minutes or until shrimp are cooked about half way, just turning pink. With a slotted spoon, transfer the sausage and shrimp to a plate.
Saute shrimp shells in the same pan used for sausage and shrimp for 5 minutes until toasted and red. Add the onion and celery, white wine, bay leaves, canned tomatoes, chicken broth, paprika and saffron, if using. Bring the mixture to a simmer. Simmer for 30 minutes and remove the shrimp shells and vegetables with a slotted spoon. Bring the broth back up to a simmer and add the clams. Cook until all are open, discarding any unopened clams. Remove clams to a tray and pour the broth into a clean pot or bowl.
Heat the original pot that the broth was in and add some olive oil. Add the green pepper, scallion whites, and garlic. Cook over moderate heat, stirring, for about 2 minutes. Add the rice and thyme and saute for about a minute and then season with salt and pepper. Add stock (3 parts stock to rice, about 9 cups of broth - if you do not have enough broth, add chicken broth and bring the mixture to a boil. Reduce the heat to a simmer, cover and cook the jambalaya rice for 20 minutes. Stir in the hot sauce and parsley and then add the shrimp, sausage and clams. Season with pepper and cook the mixture, covered, for 5 more minutes or until the shrimp are just done and the rice is tender.
Serve the jambalaya sprinkled with the reserved scallion greens.