Cook rice mix according to package directions. Add butter, thyme, onion powder, and 1 1/2 cups grapes; stir well.
Season cavity of chicken with salt, place chicken, breast side up, on a rack in a shallow roasting pan. Stuff lightly with half of rice mixture. Truss chicken, and bake at 375F for 1 1/2 hours. Combine soy sauce and wine, use to baste chicken during last 30 minutes of baking.
Spoon remaining rice mixture into a lightly greased 1-quart casserole; bake at 375F for 15 to 20 minutes. Remove chicken to serving platter, and spoon rice around it. Garmish with grapes, if desired.