Increase thickness of outlines

Hi,

I want to add another property to increase the size/thickness of the outline in the following shader:

 Shader "Custom/Sprite Outline" {
     Properties {
         _MainTex ("Base (RGB)", 2D) = "white" {}
         _Color ("Color", Color) = (1, 1, 1, 1)
     }
     SubShader {
         Tags {"Queue"="Transparent" "RenderType"="Transparent"}
         Cull Off
         Blend One OneMinusSrcAlpha
         
         Pass {
 
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #include "UnityCG.cginc"
 
             sampler2D _MainTex;
 
             struct v2f {
                 float4 pos : SV_POSITION;
                 half2 uv : TEXCOORD0;
             };
 
             v2f vert(appdata_base v) {
                 v2f o;
                 o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                 o.uv = v.texcoord;
                 return o;
             }
 
             fixed4 _Color;
             float4 _MainTex_TexelSize;
 
             fixed4 frag(v2f i) : COLOR
             {
                 half4 c = tex2D(_MainTex, i.uv);
                 c.rgb *= c.a;
                 half4 outlineC = _Color;
                 outlineC.a *= ceil(c.a);
                 outlineC.rgb *= outlineC.a;
 
                 fixed alpha_up = tex2D(_MainTex, i.uv + fixed2(0, _MainTex_TexelSize.y)).a;
                 fixed alpha_down = tex2D(_MainTex, i.uv - fixed2(0, _MainTex_TexelSize.y)).a;
                 fixed alpha_right = tex2D(_MainTex, i.uv + fixed2(_MainTex_TexelSize.x, 0)).a;
                 fixed alpha_left = tex2D(_MainTex, i.uv - fixed2(_MainTex_TexelSize.x, 0)).a;
 
                 return lerp(outlineC, c, ceil(alpha_up * alpha_down * alpha_right * alpha_left));
             }   
 
             ENDCG
         }
     } 
     FallBack "Diffuse"
 }

I am using this shader to outline a 2d sprite which has is semi-transparent.

Any help would be appreciated. Thanks