Billboard scale

Hey,
I have a shader to billboard a plane, it’s working great except it doesn’t support scaling.
here’s the vertex shader:

 v2f vert (appdata v)
            {
                v2f o;
                //Scale support but breaks position...
                //v.vertex = mul (_Object2World, v.vertex);
               
                o.pos = mul(UNITY_MATRIX_P,
        mul(UNITY_MATRIX_MV, float4(0.0, 0.0, 0.0, 1.0)) - float4(v.vertex.x, v.vertex.y, 0.0, 0.0));

                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                return o;
            }

I made some support for the scale using v.vertex = mul (_Object2World, v.vertex); but it breaks the positon in x and y.

any help would be great!
Thanks.

NVM, found my answer here:
https://en.wikibooks.org/wiki/Cg_Programming/Unity/Billboards