It may not be possible to automate it, but it's possible. trace a polyline over the existing profile and drop it down 5' in the profile view. then trace the pipes below the 5 feet line. form closed polygons and hatch them.
not dynamic but hey it works.
Civil 3D 2013 Win 7 Pro x64 Intel Xeon 2.0GHz 12Gb Ram ATI Firepro 4800 Dell T5500 www.preinnewhof.com