I know this isn't exactly what you are looking for, but try the free program named Terrain_Del on the top right side of this link:
http://arrowsoft.ifrance.com/arrowsoft/I think you'll really like it.
It uses 256x256 bmp hightmaps to produce an "infinite" terrain and four 64x64 bmp textures to map seccessive altitudes. There are specifics for making and insrting these into the program for yourself.
Somewhere on the link Vlad names the one from whom he got the primary code, so you might contact either one of them for more information.
Down in the 3dgs forum section devoted to suggestions about future features to our game I requested the ability to build a world using Terrains_Del's method.
Warning: Terrain_Del is highly addictive for those such as me who are easily amused. I used to rev it up and just cruse for hours at a time. Since one rarely approachs a feature from the same angle twice it really does look like the world is immense. Hope you like wandering the oceans and at last sighting land in the distance. It's so realistic.
If you turn up any useful information, please post it here. Maybe putting this kind of thing in 3dgs can be done very easily, and that would be nice.