How can I provide my own ICustomTypeDescriptor in ASP.NET MVC?

I'm working on a small library for for ASP.NET MVC 3 that should offer better reusability of model metadata and easy mapping from data entities from / to custom viewmodels. For this I need to be able to provide my own implementation of ICustomTypeDescriptor for three different areas of interest in ASP.NET MVC:

1. Scaffolding
2. Validation
3. Modelbinding

It seems like this could be done by setting System.Web.Mvc.ModelMetadataProviders.Current to my own CustomMetaDataProvider, but this is not nearly enough to cover all three points above.

The problem is that there are several classes in System.Web.Mvc which call directly into this System.Web.TypeDescriptorHelper which is not extensible because it looks like this:

internal static class TypeDescriptorHelper {
        public static ICustomTypeDescriptor Get(Type type) {
            return new AssociatedMetadataTypeTypeDescriptionProvider(type).GetTypeDescriptor(type);
        }
    } 

The only solution I found is very awkward and required subclassing lots of types from System.Web.Mvc to make it work. I even had to re-implement CustomModelBinderDictionary completely only to overwrite one or two lines of code. So it works, but it is a very messy hack and likely to break the next time I update to a new ASP.NET MVC version.

So here's what I like to know : Did I miss any simple way to do this?

Bonus question: If not and you are from the MVC team, could you consider creating an appropriate extensibility point in MVC 4 ;-)?

Edit: In reply to the question why I need to code my own TypeDescriptor: There are several reasons for this: 1. Most important: I need a workaround for the problem described at https://forums.asp.net/t/1614439.aspx/1 2. Also, I need to insert metadata dynamically for various reasons. For example I want to code my own Bind attribute, but BindAttribute is sealed. So instead of deriving from it, I am emitting a matching BindAttribute dynamically from the TypeDescriptor when detecting my own bind attribute implementation.

According to Brad Wilson (an ASP.NET MVC team member) this issue has been put on the bug list for MVC 4. So it seems there is no good solution for the moment, but hopefully this will be solved when MVC 4 comes out.

For anyone interested in my library for reusable validation and scaffolding metadata and model / viewmodel mapping, feel free to subscribe my blog at https://devermind.wordpress.com/. I'm going to release the library there.