Special equipment: A melon baller
Halve the oranges and gently scrape out the pulp, membrane and white pith with a spoon or melon baller. Place the orange rinds in muffin tins or fit them all into a pan so they can be filled without tipping over.
Put 1/2 cup cold water in a bowl, sprinkle the gelatin evenly on top and let it absorb the water for 2 minutes. Whisk in 3/4 cup boiling water until the gelatin is fully dissolved and then whisk in the sugar until dissolved. Cool the mixture to room temperature and then stir in the blood orange sparkling soda, tequila and orange liqueur. Spoon the gelatin mixture into the orange rinds. Refrigerate overnight.
Carefully slice each orange half into 2 wedges and serve.