Wonder if there is a way to just build the wall as part of the terrain itself, maybe using Chipp Walter's 'AltTerrain Builder'? You might have to settle for a mesh terrain, not procedural. And if so, you could also export your terrain mesh to a 3D program and build your walls there.

'Art Head Start' e-book
'Art Head Start.com site Digital Art skills. Free lighting chapter, tutes, Vue models, tex pix.