gistfile1.cs

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

namespace ConsoleApplication2
{
	using System.Runtime.Serialization;

	class Thing1
	{
		private readonly Thing2 thing2;

		public Thing1(Thing2 thing2)
		{
			this.thing2 = thing2;
		}

		public Thing2 Thing2
		{
			get { return thing2; }
		}
	}
	class Thing2
	{
		private readonly Thing1 thing1;

		public Thing2(Thing1 thing1)
		{
			this.thing1 = thing1;
		}

		public Thing1 Thing1
		{
			get { return thing1; }
		}
	}
	class Program
	{
		static void Main(string[] args)
		{
			var t1 = (Thing1)FormatterServices.GetUninitializedObject(typeof(Thing1));
			var t2 = (Thing2)FormatterServices.GetUninitializedObject(typeof(Thing2));
			typeof(Thing1).GetConstructor(new[] { typeof(Thing2) }).Invoke(t1, new object[] { t2 });
			typeof(Thing2).GetConstructor(new[] { typeof(Thing1) }).Invoke(t2, new object[] { t1 });

		}
	}
}