[OR] Site Grading -> Building A New Breakline Feature from A Feature Created by a Linear Template or Corridor

Still working on my parking lot. This is complicated - I hope I have explained it well.

My design is a Curbed lot that needs to be modeled by running a Curb and Gutter as a Template around its edge (Corridor or Linear Template) because there are too many 90 degree corners to use a Normal Corridor with Point Controls. The Sidewalk behind the curb will need some walls because the parking lot doubles back on itself and also runs along another similar Parking Area.

So I wanted to build my bottom of wall breaklines using Profile by Slope From Element to run from my back of curb to the wall outline and in other areas simply use some of the remaining back of curbs. From this, I could create my sidewalk terrain element and apply a pavement section to it and complete my 3D model.

In Ss2, I could build a new 3D breakline from a Feature in a DTM from any source (corridor, etc.) 

But the Profile by Slope From Element tool will not allow me so select the Feature from my Corridors or Linear Templates.

My parking lot edge is a derived surface from an underlying terrain from a General "pavement slope only" corridor. My design intent needs to build from that terrain, to my curbs as draped on that terrain and from there to my sidewalk edges from that back of curb.

How can I extract the back of curb features where I need them while still retaining their link to the original corridor so that this tool will allow me to create my bottom of wall?