Pick a horizontal target line for daylight?

[howitzer]

Is there a way to pick a horizontal target line for daylight?

I have a 4000' roadway with most of the cut/fill side slopes at 4:1. However, there is a 1000' section along one side where the daylight will be less than 4:1 and will vary in both horizontal and vertical measurements. What I'd like to do is draw a polyline and simply pick it as the horizontal target while having the existing surface elevation giving the vertical information.

I'm using the Road Design program to create cross-sections and contours.