It may or may not be possible. You can try adjusting render bin numbers. PlaceNodes are drawn by the ScreenSpaceLayout code, which defaults to render bin #13; you can change that using ScreenSpaceLayout::setOptions. You would also need to adjust the render bin number of the geometry (usually using a RenderSymbol).
This will only work if the placenode draws first, writing to the depth buffer and "obscuring" the line. But that assumes the line is at the same or greater depth, which is uncertain.