Peel rind and white membranes from oranges.
Slice enough rind (orange part only) to make about 3 tablespoons slivers.
Combine with sugar and water; cook over moderate heat, without stirring, about 8 minutes, until slightly thickened.
Put oranges in syrup; cook over very low heat, basting constantly, about 5 minutes, until warm but still firm.
Remove from heat with slotted spoon.
Add liqueur to syrup.
Chill oranges; baste occasionally with syrup.