Right now I working on modeling a bonnet to a car. At the upper edge of the bonnet towards the windshield, I'm planning to add a lip that can conceal the wiper blades underneath it. In order to create this lip, then I come to conclusion that I have to add a line that runs parallel to the upper edge of the bonnet. This edge is not properly half-round, it's more half-oval, which probably makes it harder to just add another circle beneath it.
Are there any tools that will be able to trace the line of the edge and add a parallel line beneath it, or do I have to do it manually?
Here is the bonnet from above:

An example of what I'm looking to model (the lip that extend upward right in front of the windshield):

The bonnet seen from the same angle as the car above. Note the lack of any upfacing lips.
