ASP.NET MVC 2 - 在IValueProvider上设置值

I am attempting to upgrade my MVC 1 project to MVC 2 RC. We currently have a custom modelbinder that adds items to the ValueProvider (this worked when it was a dictionary). We then passed this off to the default modelbinder. However, IValueProvider does not have an add method, so this algorithm no longer works. Does anyone know of a way to add values to the ValueProvider in MVC 2? I am attempting to upgrade my MVC 1 project to