Thundering - another arrow to your bow...

If you save out a height texture, then use that just as a guide, import into a 2D app, create a road-map (or watever) (in PURE Black/White), then delete the original background (IE terrain) and save JUST the B/W road-map...

You can apply that map to the terrain in Vue (well, in V5I, at least), by clicking on the the "Picture" Icon at (or near) the bottom of the LH list in the terrain editor. In the resulting dialogue, load the road-map into the RH slot.
You can adjust the amount of influence of the 2nd pic (using the controls under the 2 pics).. The road-map needs to be applied at VERY low values.. But it does affect the terrain...

This takes a lot of experimentation to get right, but sometimes works very well (other times it's an abyssmal failure).

Be warned - once you accept, the 2 pics (1 of the terrain and the second of the "Road Map" are immediately combined, and you can't undo it. And there's no easy preview to see what results, AFAIK). Lots of save-before-doing and reloading-when-it-didn't-work involved..

BUT - it does combine them..:-))

Cheers,
Diolma