Control mips in shader

Hey All, I'm trying to find a way to control the mip levels of a texture in my shader. I want to be able to blur a cubemap reflection to get a more glossy/softer reflection.

Thanks!

 Shader "WMS/Chrome" {
     Properties {
       _Color ("Main Color", Color) = (1,1,1,1)
       _SpecColor ("Specular Color", Color) = (1, 1, 1, 1)
       _RefColor ("Reflection Color", Color) = (1, 1, 1, 1)
       _Shininess ("Shininess", Range (0.03, 1)) = 0.078125
       _BumpMap ("Normal", 2D) = "bump" {}
       _Cube ("Cubemap", CUBE) = "" {}
     }
     SubShader {
       Tags { "RenderType" = "Opaque" }
 
 CGPROGRAM
 #pragma surface surf BlinnPhong
 #pragma target 3.0
       
       struct Input {
           float2 uv_BumpMap;
           float3 worldRefl;
           INTERNAL_DATA
       };
       
       samplerCUBE _Cube;
       sampler2D _BumpMap;
       fixed4 _Color;
       fixed4 _RefColor;
       half _Shininess;
       
       void surf (Input IN, inout SurfaceOutput o) {
           o.Albedo = _Color.rgb;
           o.Gloss = _SpecColor.rgb;
           o.Specular = _Shininess;
           o.Normal = UnpackNormal(tex2D(_BumpMap, IN.uv_BumpMap));
           o.Emission = texCUBE (_Cube, WorldReflectionVector (IN, o.Normal)) * _RefColor;
       }
       ENDCG
     } 
     Fallback "Specular"
   }