Only export what's on the top layer


My team and I are using Qubicle for all our models, and for creating our terrain we import a heightmap and make it into voxels. However, this is generates terrible performance, as all the voxel underneath the first layer of voxels are also getting rendered. I looked at the “Face Removal” and I understand you can toggle the faces you don’t need. However, let’s say I toggle the buttom layer, then the voxels underneath the first layer will still be rendered, just not the buttom face.
Is there anyway you can export only the top layer or the layer that’s visible for the camera?