Spray the inside of a 4 or 5-quart slow cooker with butter-flavored cooking spray.
In a large bowl, combine bread cubes, pineapple, and dried tropical mix.
In a medium bowl, whisk together coconut milk, rum, nectar, sugar, eggs, cinnamon, and salt. Pour over bread mixture. Stir until well combined and bread is saturated.
Transfer to slow cooker. Dot with butter. Cover and cook on low setting for 3 to 4 hours.