Very similar Nicos, but if you can't buy ginger ale you could always try substituting ginger beer. Did a search on the net and have come up with this recipe. Ginger "plant" as already said. They say make the beer every ten days, we used to do it every week on Saturday, but I suppose it can be adjusted.

Dissolve 18 oz (500g) of sugar in one and a half pints (900ml) of water. Bring to the boil, let cool and add the strained juice of two lemons. Add the liquid from your ginger plant to this mixture, together with another six pints (3.4 litres) of water. Stir well and bottle in sterilised strong screw topped beer bottles. Store in a cool place for at least two weeks before you drink.