Add reflection to refractive shader

Hey All,

I'm trying to figure out how to add cubemap reflections to the below shader (basically the stained glass shader from Unity Pro). Can anyone help out?

Thanks a lot!

 Shader "WMS/Glass_Refractive" {
 Properties {
     _BumpAmt  ("Distortion", range (0,128)) = 10
     _MainTex ("Tint Color (RGB)", 2D) = "white" {}
     _BumpMap ("Normalmap", 2D) = "bump" {}
     _Cube ("Cubemap", CUBE) = "" {}
 }
 
 Category {
 
     // We must be transparent, so other objects are drawn before this one.
     Tags { "Queue"="Transparent" "RenderType"="Opaque" }
 
 
     SubShader {
 
         // This pass grabs the screen behind the object into a texture.
         // We can access the result in the next pass as _GrabTexture
         GrabPass {                            
             Name "BASE"
             Tags { "LightMode" = "Always" }
          }
          
          // Main pass: Take the texture grabbed above and use the bumpmap to perturb it
          // on to the screen
         Pass {
             Name "BASE"
             Tags { "LightMode" = "Always" }
             
 CGPROGRAM
 #pragma vertex vert
 #pragma fragment frag
 #pragma fragmentoption ARB_precision_hint_fastest
 #include "UnityCG.cginc"
 
 struct appdata_t {
     float4 vertex : POSITION;
     float2 texcoord: TEXCOORD0;
 };
 
 struct v2f {
     float4 vertex : POSITION;
     float4 uvgrab : TEXCOORD0;
     float2 uvbump : TEXCOORD1;
     float2 uvmain : TEXCOORD2;
 };
 
 float _BumpAmt;
 float4 _BumpMap_ST;
 float4 _MainTex_ST;
 float3 worldRefl;
 
 v2f vert (appdata_t v)
 {
     v2f o;
     o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
     #if UNITY_UV_STARTS_AT_TOP
     float scale = -1.0;
     #else
     float scale = 1.0;
     #endif
     o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y*scale) + o.vertex.w) * 0.5;
     o.uvgrab.zw = o.vertex.zw;
     o.uvbump = TRANSFORM_TEX( v.texcoord, _BumpMap );
     o.uvmain = TRANSFORM_TEX( v.texcoord, _MainTex );
     
     return o;
 }
 
 sampler2D _GrabTexture;
 float4 _GrabTexture_TexelSize;
 sampler2D _BumpMap;
 sampler2D _MainTex;
 samplerCUBE _Cube;
 
 half4 frag( v2f i ) : COLOR
 {
     // calculate perturbed coordinates
     half2 bump = UnpackNormal(tex2D( _BumpMap, i.uvbump )).rg;
     float2 offset = bump * _BumpAmt * _GrabTexture_TexelSize.xy;
     i.uvgrab.xy = offset * i.uvgrab.z + i.uvgrab.xy;
     
     half4 col = tex2Dproj( _GrabTexture, UNITY_PROJ_COORD(i.uvgrab));
     half4 tint = tex2D( _MainTex, i.uvmain );
     return col * tint;
 }
 ENDCG
         }
     }
 
     // ------------------------------------------------------------------
     // Fallback for older cards and Unity non-Pro
     
     SubShader {
         Blend DstColor Zero
         Pass {
             Name "BASE"
             SetTexture [_MainTex] {    combine texture }
         }
     }
 }
 
 }