There is a lovely recipe for wild service vodka (Aufgesetzten aus Elsbeeren) here:
The German word Aufgesetzten does not appear to have an exact English translation, but having spoken to several fluent German speakers it seems to mean something like a 'pick-me-up' or, as my Northumbrian friend David Copeland would have said, a 'livener'. It seems that one could make Aufgesetzten with any spirit and any fruit, though wild service berries should be particularly good as they combine apricot flavours from the fruit pulp and almond flavours from the seeds.
The recipe is at the end of the web site referenced above and I have translated it as follows:
To make the Aufgesetzten pound 400 grams of wild service berries in a non-metallic vessel. Let the pounded pulp stand and ferment in a warm place for a week then put the pulp in a linen cloth (jelly bag) and squeeze the juice out.
Mix the juice with an equal quantity of vodka (at least 40% alcohol by volume), then mix the remaining pulp with 1/4 litre of vodka and filter the liquid off from this after two weeks.
Mix the two juices together and stir in three tablespoons of honey.
Leave at room temperature for one year before drinking.
One problem here is that the recipe does not specify whether the berries should be in their unripe and hard condition, or soft and ripe - probably the latter -though, if you can afford the vodka, it might be worth trying both and also experimenting with the fruit of other Sorbi.