If I understand the question, you want to have the same slope of terrain the track has, but also adjacent and parallel to the track? Two ways I have done.
1. Lay temporary parallel track segments to the new track. Make the top and bottom elevations the same as the new track. Smooth the parallel segments, then delete the unneeded track.
2. Use the copy and paste tool with only the terrain height selected. Copy a 10m x ?m selection of the track, then paste 10m to the side.
