Combine 150 g (5 oz) of the blueberries with the alcohol in a bowl and leave to soak for at least 1 hour. Then mash the blueberries.
Beat together the mascarpone and yogurt in a separate bowl until smooth, then mix in the sweetener and the lime rind and juice.
Layer alternate spoonfuls of mashed blueberries and mascarpone in 4 glasses. Top with the whole blueberries and chill until ready to serve.