Working on a two passes material, the shadow pass being potentially added automatically in the material by enabling shadows.

Here is how it looks:

material two_pass_shadows
{
  receive_shadows on

  technique
  {
    
    shadow_caster_material shadowscaster
    
    pass standard
    {
      ambient 0.0 0.0 0.0 1.0
      diffuse 0.8 0.8 0.8 1.0
      specular 0.0 0.0 0.0 1.0 0.0
      emissive 0.0 0.0 0.0 1.0
      alpha_to_coverage off
      colour_write on
      cull_hardware clockwise
      depth_check on
      depth_func less_equal
      depth_write on
      illumination_stage
      light_clip_planes off
      light_scissor off
      lighting on
      normalise_normals off
      polygon_mode solid
      scene_blend one zero
      scene_blend_op add
      shading gouraud
      transparent_sorting on
      
      // SUPER IMPORTANT TO AVOID FLICKERING
      depth_bias 0 -1
      
      texture_unit
      {
        texture rock.jpg
        tex_address_mode wrap
        scale 1 1
        colour_op modulate
      }
      
    }
    
    pass pssm
    {
      scene_blend add
      
      // SUPER IMPORTANT TO AVOID FLICKERING
      depth_bias 0 0
      
      vertex_program_ref ShadowsPssm_vert
      {
      }
      fragment_program_ref ShadowsPssm_pix
      {
      }
      texture_unit
      {
        content_type shadow
        tex_address_mode border
        tex_border_colour 1 1 1 1
      }
      texture_unit
      {
        content_type shadow
        tex_address_mode border
        tex_border_colour 1 1 1 1
      }
      texture_unit
      {
        content_type shadow
        tex_address_mode border
        tex_border_colour 1 1 1 1
      }
    }
    
  }
}

There is still issue with wireframe materials for instance ( polygon_mode wireframe ). Another issue is the poor definition of the shadows once the camera is a bit further.

As shown in this image, there is a clear cut in definition when going from the near texture (green one, 2048) to the second one (red one, 1024). I guess I have to look much closer to the distance steps.