Thanks for the suggestion. We will evaluate that for a future release. Have you tried "Road Preference: Scenic Route"? While it won't do exactly what you are asking, it should increase the chance that you will be routed over small roads as opposed to highways.
I have used the Scenic Routes Preference. In combination with Shortest time It still wants to prefer Interstates in many cases. The combination of Scenic Route and Shortest route gives me much longer routes and bizarre side trips along the route.
