Blended mesh with lighting ?

Hi there,

I have something I can’t figure out yet. I have a mesh of a terrain which displays great with lighting enabled (because of the lighting I can see the difference in height).
Now I am trying to make the same mesh half transparent so I can see thing under the mesh (aka ground).

If I enable blending I seem to loose my lighting, the whole Mesh is rendered with a half transparent flat color.
Although I now see the objects under the ground I lost the depth appearance of the mesh.

Is there any way to preserve the lighting while doing blending or do I have to use some sort of multipass rendering ?

Thanks in advance,

the Hague, the Netherlands