Thaw roast in refrigerator for 24 to 48 hours.
Remove roast from refrigerator, pat dry with paper towels, and allow to come to room temperature; about 30 minutes.
With a sharp boning knife, make a 2-inch lengthwise incision in the middle of both sides of the roast. Place fingers through each hole to ensure incisions connect in the middle. Using a spoon, fill the middle of roast with sausage stuffing.
Drizzle roast with 2 tablespoons grapeseed oil and liberally season with Italian rub.
Preheat oven to 250 degrees Fahrenheit.
Place remaining grapeseed oil in a cast-iron pan on medium-high heat and sear roast on all sides EXCEPT the ends where the stuffing is; about 1 and a half minutes on each side.
Place stuffed roast on a wire-rack-lined baking sheet and cook for about 1 hour to 1 hour and 15 minutes, until internal temperature reads 140 degrees Fahrenheit. Rest for about 15 minutes for perfect medium doneness of 145 degrees Fahrenheit. If you desire greater cooking doneness, refer to the Omaha Steaks cooking chart.