Both targets (32 and 64bits) at same time ?

%PROGRAMFILES%\CommonAppFolder
   \x64
      main_binary_x64.exe (references to x64 version of Graphics Mill)
      Aurigma.GraphicsMill.dll (x64 version)
   \x86
      main_binary_x86.exe (references to x86 version of Graphics Mill)
      Aurigma.GraphicsMill.dll (x86 version)

And 2 shortcuts somewhere in Start menu: 
      TheApp (x86): %PROGRAMFILES%\CommonAppFolder\x86\main_binary_x86.exe
      TheApp (x64): %PROGRAMFILES%\CommonAppFolder\x64\main_binary_x64.exe

namespace DualPlatformApp
{
	class Program
	{
#if __X64 //this constant is defined in project options for x64 configuration only
		private const string gmAssemblyPath = @"\aurigma_x64\Aurigma.GraphicsMill.dll";
#else
		private const string gmAssemblyPath = @"\aurigma_x86\Aurigma.GraphicsMill.dll";
#endif
		static Program()
		{
			AppDomain.CurrentDomain.AssemblyResolve += new ResolveEventHandler(OnAssemblyResolve);
		}

		static Assembly OnAssemblyResolve(object sender, ResolveEventArgs args)
		{
			Assembly result = null;
			if (args.Name.StartsWith(@"Aurigma.GraphicsMill, Version=5.5.2.0, Culture=neutral, PublicKeyToken=af7154c50c505858"))
			{
				result = Assembly.LoadFrom(
					Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location) + gmAssemblyPath);
			}
			return result;
		}
		
		static void Main(string[] args)
		{
			Assembly gmAssembly = Assembly.GetAssembly(typeof(Aurigma.GraphicsMill.Bitmap));
			System.Console.WriteLine("\nThis binary references: " + gmAssembly.Location);
		}
	}
}