Reselect your "front" compound path, make a copy in front (Control-C > Control-F), select it and replace the existing fill color with R=237 G=170 B=37. Move to the Layers panel and rename this new shape "back". Select it along with your "3D" shape, make sure that the Selection Tool (V) is active, click on your "3D" shape (it should get emphasized), and then open the Align pane (Window > Align) and click the Vertical Align Bottom button. In the end your "back" shape should be placed as shown in the third image. Make sure that it's still selected and simply hit Control-[ to send it behind your "front" shape, as shown in the fourth image.