AutoCAD Civil 3D :: Shoulder Subassembly That Varies Slope In Relation To Lane Superelevation Slope

i need a shoulder subassembly that varies slope in relation to the lane superelevation slope. i know that i can get a subassembly for the shoulder that will follow the alignment superelevation xml data but in my case i can't use it because we are just adding a shoulder to an existing road. we're not changing the superelevation of the existing road, just milling and overlaying and widening. right now i've created a profile of the outside edge of the shoulder that gives me the correct shoulder slope but whenever i change my centerline profile i have to redo the shoulder profiles which is a real time suck.