Adding a line to a 3D Column Chart

Hello All

I am wondering if it is possible to add a horizontal line to a 3D column chart. I have found a link to a page that Andy Pope has put together (http://www.andypope.info/charts/averageline.htm), it explains how this can be done with 2D charts (which I have managed to follow without any problem) but when I try this using a 3D column chart it doesn't seem to work.

Does anyone know if this is possible?

Thanks in advance

Jim