Using the sauté function, heat the oil in the pressure cooker pot. Stir in the sausage and cook until well browned, 5 to 7 minutes. Use a slotted spoon to transfer the sausage to a plate.
Stir in the onion, bell peppers, celery, sliced garlic, 1 teaspoon of the salt, the sage, black pepper, and cayenne. Cook until the vegetables are soft and just starting to brown, about 7 minutes. Stir in the bay leaves, thyme, beans, 31/2 cups water, and remaining 1 ¼ teaspoons salt.
Lock the lid into place and cook on high pressure for 15 minutes. Let the pressure release naturally.
Remove the thyme sprigs and bay leaves. Use a slotted spoon to remove two thirds of the beans, and set them aside. With an immersion or regular blender, puree the remaining beans in the pot to thicken the mixture.
Turn on the sauté function. Stir in the sausage and the reserved beans, bring the entire mixture to a simmer, and cook for 3 to 5 minutes, or until the mixture has thickened to your liking.
Taste and add more salt if needed and season with lemon juice to taste. Serve the beans and sausage over rice, topped with scallions, chopped celery leaves, and hot sauce.