Sausage-Stuffed Rack of Pork with Sage

Preheat oven to 500 °F with rack in middle. Partially cut roast away from bones to create a "flap" (for stuffing, allowing meat to be returned to bone). Rub pork inside and out with 1 1/2 teaspoons salt and 1/2 teaspoon pepper, then rub outside with 1 teaspoon oil. Put sage, then sausages and scallions, inside flap and tie roast with string. Put roast, bone side down, in a large roasting pan with celery and olives, then pour in wine and remaining cup oil. Roast 20 minutes, then reduce heat to 325 °F and roast, basting meat every 30 minutes, until an instant-read thermometer inserted into center of meat (do not touch bone) registers 155 °F, about 2 hours more. Let stand 15 minutes. Serve with pan juices.