Nowhere in the Civil 3D Help system is there reference to the AECLINEWORKSHRINKWRAP command. This command is present in Land Desktop and is described in Land Desktop Help. You can use it in Civil 3D 2005.
To use it enter AECLINEWORKSHRINKWRAP at the command line. It then prompts you to "Select object(s) to generate shrinkwrap from:". Select object(s) and press Enter. A new Polyline will be created on the current layer from the silhouette/outline of the selected objects.
The command can also be entered after you have selected objects in Noun/Verb mode.