gistfile1.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;
using Jurassic;
using Jurassic.Library;

namespace NotActuallyTheDlrCoffee
{
    public class CoffeeScriptCompiler
    {
        [ThreadStatic] ScriptEngine _engine;
        ScriptSource _coffeeScriptCode;

        public string Compile(string coffeeScriptCode)
        {
            if (_engine == null) {
                _engine = initializeCoffeeScriptEngine();
            }

            return _engine.CallGlobalFunction<string>("compilify", coffeeScriptCode);
        }

        ScriptEngine initializeCoffeeScriptEngine()
        {
            if (_coffeeScriptCode == null) {
                var ms = new MemoryStream();
                Assembly.GetExecutingAssembly().GetManifestResourceStream("NotActuallyTheDlrCoffee.lib.coffee-script.js").CopyTo(ms);

                var str = Encoding.ASCII.GetString(ms.GetBuffer());
                _coffeeScriptCode = new StringScriptSource(str.Replace('\0', ' '));
            }

            var ret = new ScriptEngine();
            ret.Execute(_coffeeScriptCode);

            const string compilifyFunction =
                @"function compilify(code) { return CoffeeScript.compile(code, {bare: true}); }";

            ret.Execute(compilifyFunction);
            return ret;
        }
    }
}

Add the browser version of coffee-script.js as an Embedded Resource to use this