Making a character appear through 1 layer of objects but not 2 or more

Hi,

I am working on a project using Kinect and Zigfu. I have a Kinect feed object (a flat screen between the main camera and the rest of the scene) through which I want my character to appear. This works pretty well, I have written the following shader to achieve this:

     Properties {
         _Color ("Main Color", Color) = (1,1,1,1)
         _MainTex ("Base (RGB)", 2D) = "white" {}
     }
     Category {
         SubShader {
       
             //sampler2D _MainTex;
           
             Tags { "Queue"="Overlay+1" }
                                           
              Pass
             {
                 ZTest Greater
                 Lighting Off
                 SetTexture [_MainTex] {combine texture}
             }
                                           
             Pass
             {
                 ZTest Less
                 SetTexture [_MainTex] {combine texture}
             }
           
             CGPROGRAM
             #pragma surface surf Lambert
 
             sampler2D _MainTex;
             fixed4 _Color;
 
             struct Input {
                 float2 uv_MainTex;
             };
 
             void surf (Input IN, inout SurfaceOutput o) {
                 fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
                 o.Albedo = c.rgb;
                 o.Alpha = c.a;
             }
             ENDCG
         }
     }
     FallBack "VertexLit"
 }

However, if there is an object between this Kinect screen and the character, I want that part of the character to be occluded. Right now, the character appears through everything regardless of the number of objects standing between it and the camera. Is there a way for the character to only be rendered with 1 or less objects being between it and the camera? I have also read that I could add a second Z buffer or something, would that be a better solution?

Also I think the CPROGRAM part of my shader is not doing anything. I included that as I wanted phong/specular shading applied to my model but right now it seems as though I am only getting diffuse. Any help with this would also be greatly appreciated.

I'll answer any questions and provide more info if that makes it any easier.