Preheat the slow cooker if necessary; see the manufacturer's instructions. Strain the lime juice into the slow cooker pot and discard the pips. Add the rum, ginger wine, water and sugar, cover and cook on high for 1 hour.
Reduce the heat to low and cook for 2–3 hours until the punch is piping hot or until you are ready to serve. Stir well, then ladle into heatproof glasses and add a slice of lime and 2 pieces of pineapple to each glass.