Put the shallot, vinegar and sugar in a small saucepan. Bring to a boil and cook 5 minutes. Remove and cool. Transfer to a small bowl for serving. Open the oysters and loosen the muscles from the hinges. Arrange the oysters on the half shell on a platter and serve immediately, passing the pickled shallot for those who want it. A few lemon wedges for those who prefer their oysters' plain is a nice thought, too.