CreateInterface.cs

using System;
using System.Reflection;

interface ILoveCats
{ }

class Program
{
	static void Main(string[] args)
	{
		var allocate = typeof(RuntimeTypeHandle).GetMethod("Allocate", BindingFlags.NonPublic | BindingFlags.Static);

		var cat = allocate.Invoke(null, new[] { typeof(ILoveCats) });

		Console.WriteLine(cat.GetType()); // ILoveCats
	}
}