If you dilute the jam to get a working specific gravity you can use a high tolerance wine yeast to make a great strong wine. Keep adding a couple of ounces of sugar syrup to the fermentation every 21 days once the initial fermentation is nearly over or so till the wine stops fermenting of it's own accord this time next year.
Rack it off and add a pint of quality brandy , then store in bulk at say 4 gallons and leave to mature another year. Check for quality then bottle in small bottles .. you will have a great liqueur type substance in a really rich black current colour that is as clear as a bell & still fairly high in vitamin C .
Store in a cool dark place & consume within five more years or it will develop a sulpherous off flavours .
Do be aware that drinking lots of very high sugar can and frequently turn you into a type 2 diabetic .. ( That was my route to diabetes )