Check out the latest in Autodesk Labs and the best part, the software is FREE. This tool was deleloped to modify or build custom subassemblies without .NET knowledge.
The technology preview release provides a strong set of subassembly functionality for corridor modeling:
■ Define points and position them based on several positioning methods.
■ Define links between points.
■ Assign codes.
■ Define targets and input parameters.
■ Specify conditions for daylight and simple expressions.
Video link is provided for quick overview; http://www.youtube.com/watch?v=VnNO9vzxp6A
Login to Autodesk Labs; http://labs.autodesk.com/
Link to subassebly creater; http://labs.autodesk.com/utilities/civil3d_subassembly_editor/