The sauce can be made up to 2 days ahead and warmed in the microwave just before serving. You'll get a lot of liquid from the pears after they macerate in the sugar overnight. This sauce is also good served over pound cake.
Combine pears and sugar in a zip-top plastic bag; shake well. Seal and refrigerate 8 hours or overnight.
Place 2 tablespoons lemon sections in a medium saucepan; reserve remaining lemon sections for another use. Add pear mixture, walnuts, raisins, cherries, and orange to pan. Bring to a simmer over medium heat; cook 30 minutes or until mixture is thick and slightly soft, stirring occasionally. Serve over ice cream.