ASP.NET MVC - Model binding a set of dynamically generated checkboxes - how to

I'm trying to model bind a set of dynamically generated checkboxes so as to process them in the controller action but can't get the model binding to occur. This is the scenario:

My ViewModel class (DocumentAddEditModel) contains a dictionary (Dictionary<string,bool>) with the string of each entry being the name/label for each checkbox and the boolean indicating whether the checkbox is checked:

    public class DocumentAddEditModel
    {
        ...
        private Dictionary<string, bool> _categoryCheckboxes = new Dictionary<string,bool>();
        ...

        ...
        public Dictionary<string, bool> CategoryCheckboxes
        {
            get { return _categoryCheckboxes; }
            set { _categoryCheckboxes = value; }
        }
        ...
    }
}

Within my controller the action that handles the GET request for the form populates the dictonary as follows:

public class DocumentsController : Controller
{
    [RequiresAuthentication]
    [AcceptVerbs(HttpVerbs.Get)]
    public ActionResult Add()
    {
        DocumentAddEditModel documentAddEditModel = new DocumentAddEditModel();
        ...
        Dictionary<string, bool> categoryCheckboxes = new Dictionary<string, bool>();
        ...
        string[] categories = Enum.GetNames(typeof(Category));

        foreach (string category in categories)
            categoryCheckboxes.Add(category, false);

        documentAddEditModel.CategoryCheckboxes = categoryCheckboxes;

        return View(documentAddEditModel);
    }
}

Within the view i have the following to generate the checkboxes:

<% foreach (KeyValuePair<string, bool> categoryCheckbox in ViewData.Model.CategoryCheckboxes)
    {%>
    <input class="checkbox" type="checkbox" name="CategoryCheckboxes[0].Key" id="<%= categoryCheckbox.Key %>" />
    <label class="categoryLabel" for="<%= categoryCheckbox.K