When creating a gravity sewer network we need the ability to create cast in place manholes for connection to existing sewer mains. In this case the manhole needs to reference the invert of the pipe that it is connecting to. Our workaround has typically been to insert a structure that doesn’t connect to the existing pipe, because it will ruin display and pipe labels that are used in existing conditions. Then we add dummy sections of pipe or simply edit the pipe label for the connection structure. This leaves lots of room of error and defeats the whole purpose of Civil 3D which is to be completely dynamic, and to have labels that update when pipe or structures are modified.
I doubt this post will get much attention due to the fact that the people designing this software have little experience creating construction documents.