Use Conditional Cut/Fill Subassembly and attach "DaylightMultiIntercept" to force Cut in this Fill situation.
Note: In the Subassembly Properties set the "Intercept Number" to 1 (or it will keep cutting through EG).
Set the Cut Slope to desired slope (this example is 1:50 or 2%).
End result. (In cross section it will just become a smooth 2% off the boulevard, so subassembly caption may be somewhat misleading).
C3D 2018.1
C3D 2016 SP4
Win 7 Professional 64 Bit