final IGaService gaService = Graphiti.getGaService();
Polygon polygon;
{
int xy[] = new int[] { 0, 20, 20, 0, 40, 20, 20, 40, 0, 20 };
final Polygon invisiblePolygon = gaService.createPolygon(containerShape, xy);
invisiblePolygon.setFilled(false);
invisiblePolygon.setLineVisible(false);
gaService.setLocationAndSize(invisiblePolygon, context.getX(), context.getY(), width, height);
// create and set visible polygon inside invisible polygon