Only Mathew can say if it will work for his scenario, but its certainly a "left field" idea thats plausible.
Your idea is this:
Create a Horizontal alignmnet along the proposed pipe path.
Create an existing surface profile along the path. Then design a profile along the path that approximately replicates the desired vertical geometry of the proposed pipe profile. (this is the tricky step of course...)
Then use the Horizontal and proposed vertical alignment to create a Site Modeler surface. Using Comp section with a left and right offset and zero slope would do this pretty quickly. There are other methods of creating the surface (as you are aware).
Then use this surface as the pipe reference surface in the Water/Sewer tools.
If the pipe length is used as the elevation interval when creating the pipe profile in Water/Sewer, then the elevations gained would be at the ends and the pipe deflection angles at each joint are immediately available through the Water>Edit Profile tool.
Very good idea!