Hack to access UV3 attribute as vec4 in ShaderForge

ReplaceUV3Property.cs

using UnityEngine;
using UnityEditor;
using System.Collections;
using System;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

/**
 *	Provides a quick and dirty path to access a mesh.uv3 channel as Vector4 in ShaderForge
 *	To use in ShaderForge:
 *	- create a UV input set to channel 2, but do not connect to anything.
 *	- create a new vector4 property, and name it "TEMP_UV3_CHANNEL"
 *	- build your shader as normal
 *	- select the compiled shader in unity and run "Tools/ShaderForge/Replace UV3 Channel Property"
 */
public class ReplaceUV3Property : Editor
{
	[MenuItem("Tools/ShaderForge/Replace UV3 Channel Property")]
	static void Init()
	{
		Shader shader = Selection.objects.FirstOrDefault(x => x != null && x is Shader) as Shader;

		if(shader == null)
		{
			Debug.LogWarning("No Shader Selected");
			return;
		}

		string path = AssetDatabase.GetAssetPath(shader);

		string source = File.ReadAllText( path );

		// remove sf metadata
		string[] split = source.Split(Environment.NewLine.ToCharArray());
		int index = Array.FindIndex(split, x => x.StartsWith("/*SF_DATA"));
		
		source = string.Join(Environment.NewLine, split.Skip(index + 1).ToArray());

		source = Regex.Replace(source, "uniform float4 _TEMP_UV3_CHANNEL;", "");
		source = Regex.Replace(source, Regex.Escape("_TEMP_UV3_CHANNEL (\"TEMP_UV3_CHANNEL\", Vector) = (0,0,0,0)"), "");
		source = Regex.Replace(source, "_TEMP_UV3_CHANNEL", "i.uv2");
		source = Regex.Replace(source, "float2 uv2", "float4 uv2");
		source = Regex.Replace(source, "float2 texcoord2", "float4 texcoord2");
		string name = Regex.Match(source, "Shader\\s\".*\"\\s{").Value.Replace("Shader \"", "").Replace("\" {", "");
		source = Regex.Replace(source, "Shader\\s\".*\"\\s{", "Shader \"" + name + "_UV3_Vec4_Enabled\" {");

		string regexed = AssetDatabase.GenerateUniqueAssetPath(path);

		File.WriteAllText(regexed, source);

		AssetDatabase.Refresh();

		EditorGUIUtility.PingObject( AssetDatabase.LoadAssetAtPath<Shader>(regexed) );
	}
}