Follow the steps below to achieve the requirement:
1. Create the volume with a gap of about 1 average element edge length above the node/elem face.
2. Do an ESURF on the top of the node/elem face and also on the bottom face of the volume.
3. Manually create triangular face elements connecting the edge of the node/elem region to the edge of the bottom face of the volume. This needs to make volume that is completely enclosed by the face elements.
4. Use FVMESH on that set of face elements to generate tet volume elements that connect the two “faces”