Line 2 large trays with baking paper. Crumble fruitcake into a large bowl. Drizzle with rum. Mix.
Microwave dark chocolate on medium-high (75%) for 1 minute 30 seconds to 2 minutes and stir it until smooth. Or place in a glass bowl inside a pan with just enough water to make the bowl float without it coming in over the sides until the chocolate melts.
Add melted chocolate to fruitcake mixture. Mix well to combine.
Roll about 15ml of the chocolate and fruitcake mixture into a ball. Roll in sprinkles, coconut or biscuits. Place on prepared tray. Repeat with remaining fruitcake mixture and sprinkles.
Refrigerate for 1 hour or until firm. Serve.