With OpenRoads, prior to using the following tool you'll need a representation of the terrain model in each element's profile model. So you'll need the terrain model to already be set as active, or you need to project that terrain model onto the plan elements' profile model.
For each plan element you can use the Vertical Geometry tool called Profile Offset Transition, then name and export that new profile element, and you know the rest.
Alternatively, you may be able to find a way to translate the entire terrain model vertically by X meters and project that terrain model. Doing so would reduce the burden of making an offset copy on each element.
Alternatively again, you may be able to set up a VBA macro using tools that I'm not familiar with.