In a pot, boil the sugar and water until the sugar has dissolved. Add the juices and bring to the boil, then whisk in the agar agar. Boil for 90 seconds to activate it.
Pour into a tray and allow to set in the fridge. Once set, transfer to a Thermomix jug, add the sugar syrup and blend until smooth. Reserve in a piping bag and refrigerate until needed.