Manual model binding with .Net Mvc

I'm wondering if there is a way to use the built in model binding similar to the internal model binding that occurs before a controller action.

My problem is that I want to be able to control the binding as I won't know the type of object to bind until I'm actually in the context of the controller action.

I understand I can inherit the DefaultModelBinder to perform custom binding, but I'm happy with what's already on offer, and just want to utilise it - take this ideal example to get an idea of what I'm after:

public ActionResult DoCustomBinding(string modelType)
{
    ... // logic to determine type to check and create strong 'actual' type

    object model = BindModel(actualType);

    ... // do something with bound model

    return View();
}

I've looked into using the DefaultModelProvider but unsure if this is the right way of going about this and I wasn't sure how to obtain the ModelBindingContext.