Preheat oven to 425°.
Unroll roast; trim fat. Reroll roast; secure at 1-inch intervals with heavy string. Combine Spiced Plum Butter and next 6 ingredients (Spiced Plum Butter through garlic) in a bowl. Reserve 1/4 cup plum mixture; set aside.
Place the roast on a broiler pan coated with cooking spray. Insert a meat thermometer into thickest portion of roast. Brush 2 tablespoons of remaining plum mixture over roast. Bake at 425° for 50 minutes or until meat thermometer registers 160° (slightly pink). Baste occasionally with remaining plum mixture. Let stand 5 minutes before slicing. Strain pan drippings through a sieve into a bowl, reserving 2 tablespoons. Discard remaining liquid and solids. Combine reserved 1/4 cup plum mixture, pan drippings, and water in a small saucepan. Bring to a boil; reduce heat, and simmer 2 minutes. Serve sauce with roast, and garnish with plum slices and sage sprigs, if desired.