Selecting custom output cache provider for specific controller actions

I'm trying to implement a MongoDB / Memory combined Output Cache Provider to use with MVC4. Here is my initial implementation:

public class CustomOutputCacheProvider : OutputCacheProvider
{
    public override object Get(string key)
    {
        FileLogger.Log(key);
        return null;
    }

    public override object Add(string key, object entry, DateTime utcExpiry)
    {
        return entry;
    }

    public override void Set(string key, object entry, DateTime utcExpiry)
    {
    }

    public override void Remove(string key)
    {
    }
}

And my web config entry:

<caching>
  <outputCache defaultProvider="CustomOutputCacheProvider">
    <providers>
      <add name="CustomOutputCacheProvider" type="MyApp.Base.Mvc.CustomOutputCacheProvider" />
    </providers>
  </outputCache>
</caching>

And the usage within HomeController:

[OutputCache(Duration = 15)]
public ActionResult Index()
{
    return Content("Home Page");
}

My problem is, when I check the logfile for the keys that are requested, I see not only the request to home controller, but all other paths as well:

a2/  <-- should only log this entry
a2/test
a2/images/test/50115c53/1f37e409/4c7ab27d/50115c531f37e4094c7ab27d.jpg
a2/scripts/jquery-1.7.2.min.js

I've figured that I shouldn't set the CustomOutputCacheProvider as the defaultProvider in Web.Config, what I couldn't figure out is how to specify the cache provider that I want to use for a specific controller action.

With Asp.Net Web Pages you can accomplish it by using <%@ OutputCache Duration="60" VaryByParam="None" providerName="DiskCache" %> at the top of the page, but for MVC the only solution I could find is to override HttpApplication.GetOutputCacheProviderName Method in Global.asax.

Is there a more elegant way to accomplish this by using the [OutputCache] attribute?