Yeah, I am pretty bored.

gistfile1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace PHPrB64
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = "echo('hi');";
            int Levels = 20;
            string output = PHPProcess(input);
            for (int i = 0; i < Levels; i++)
            {
                output = PHPProcess(output);
            }
            Console.Write("<?php "+output+" ?>");
            Console.ReadLine();
        }
        static public string PHPProcess(string code)
        {
            string o = "eval(base64_decode('";
            o += EncodeTo64(code);
            o += "'));";
            return o;
        }
        static public string EncodeTo64(string toEncode)
        {
            byte[] toEncodeAsBytes = System.Text.ASCIIEncoding.ASCII.GetBytes(toEncode);
            string returnValue= System.Convert.ToBase64String(toEncodeAsBytes);
            return returnValue;
        }
    }
}