Stone the plums, cut off the ends from the figs and wash both well. Puree both types of fruit in a blender. Mix in the preserving sugar and let it steep for 3 hours. Stir in the juice and gingerbread spice and cook for 3 minutes according to the instructions on the packet. Pour the jam into clean, boiled glasses. Spread the rum in the lids and close the glasses tightly with the lids.