On a work surface, cut off and discard the ends of the lemons. Cut the fruit into very thin slices.
In an 8-inch (20 cm) glass dish, combine the water, sugar and corn syrup. Microwave for 3 to 4 minutes or until the sugar dissolves. Add the lemon slices. Continue cooking in the microwave for 10 minutes or until the slices become slightly translucent. Let cool.
Cover and refrigerate for 3 hours or until completely chilled. Drain and use as cake decoration, if desired.