Create ETag filter in ASP.NET MVC

I would like to create an ETag filter in MVC. The problem is that I can't control the Response.OutputStream, if I was able to do that I would simply calculate the ETag according to the result stream. I did this thing before in WCF but couldn't find any simple idea to do that in MVC.

I want to be able to write something like that

[ETag]
public ActionResult MyAction()
{
    var myModel = Factory.CreateModel();
    return View(myModel);
}

Any idea?