AutoCAD Civil 3D :: Assign Subassembly To Certain Station Range?

I have a sidewalk project with 5' wide sidewalk and the edge of sidewalk is 5' of the back of curb.  All is fine and well, I have link slope to surface subassembly assigned to one side and a link offset and slope subassembly to the other side of the sidewalk.  Everything daylights nicely.

Here is the issue......my link slope to surface subassembly is an 8:1 slope to tie into the existing surface model.  There is one stretch of sidewalk where I have a retaining wall behind the sidewalk for about 15'.  My section views are every 10' and in one of them the wall needs to show up.  I could use the link vertcial sub assembly in this area but I am not sure how to use a specific subassembly in one area.  Do I split that region up in my corridor, create a new region to use that references a new assembly to use in that 15' strectch which would contain the link vertical subassembly?  Or, do I create the link vertcial  subassembly in my current assembly and assign a station range to it so it doesn't show up throughout the entire corridor?  It's like I wante to transition in and back out of a subassembly.  Incidentally, I have one assembly used for the entire length of my project.