DataAnnotations validation in Custom Model Binder

Question

I have written a custom model binder for List in my MVC project however I am now stuck in how to get this binder to validate against my DataAnnotations validation attributes.

I have found some posts on the interwebs that talk about similar scenarios, but I haven't been able to find anything that works for my particular scenario.

Model Binder Code:

    public class QuestionModelBinder : IModelBinder
{
    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        List<QuestionEditModel> res = new List<QuestionEditModel>();
        var form = controllerContext.HttpContext.Request.Form;
        int i = 0;
        while (!string.IsNullOrEmpty(form["Questions[" + i + "].QuestionID"]))
        {
            var p = new QuestionEditModel();
            p.QuestionID = form["Questions[" + i + "].QuestionID"];
            p.Answer = form["Questions[" + i + "].Answer"];
            p.AnswerRequired = (form["Questions[" + i + "].AnswerRequired"] == "True") ? true : false;
            p.completedBy = form["Questions[" + i + "].completedBy"];
            p.completedOn=NullableParser.ParseNullableDateTime(form["Questions[" + i + "].CompletedOn"]);
            p.DefaultText = form["Questions[" + i + "].DefaultText"];
            p.EntryType = form["Questions[" + i + "].EntryType"];
            p.HelpText = form["Questions[" + i + "].HelpText"];
            p.OptionRequired = (form["Questions[" + i + "].OptionRequired"] == "True") ? true : false;
            p.OptionValue = NullableParser.ParseNullableInt(form["Questions[" + i + "].OptionValue"]);
            p.QuestionName = form["Questions[" + i + "].QuestionName"];
            p.QuestionText = form["Questions[" + i + "].QuestionText"];
            res.Add(p);
            i++;
        }

        return res;
    }

    private bool HasGenericTypeBase(System.Type type, System.Type genericType)
    {
    while (type != typeof(object))
    {
        if (type.IsGenericType && type.GetGenericTypeDefinition() == genericType) return true;
        type = type.BaseType;
    }

    return false;        
    }

}

My Model MetaData:

    [MetadataType(typeof(QuestionEditModelMetaData))]
public partial class QuestionEditModel { }


public class QuestionEditModelMetaData
{
    [Required]
    public string QuestionID { get; set; }
    [Required]
    public string QuestionName { get; set; }
    [Required]
    public string QuestionText { get; set; }
    [Required]
    public string DefaultText { get; set; }
    [Required]
    public string EntryType { get; set; }
    [Required]
    public string HelpText { get; set; }

    public Boolean AnswerRequired { get; set; }
    public Boolean OptionRequired { get; set; }

    //[RequiredIfTrue("AnswerRequired")]
    [Required]
    public string Answer { get; set; }

    [RequiredIfTrue("OptionRequired")]
    public int? OptionValue { get; set; }

    public string completedBy { get; set; }
    public DateTime? completedOn { get; set; }

    public List<Option> options { get; set; }

}

The RequiredIfTrue attribute is from the MVC Foolproof Validation library. Apparently it isn't quite foolproof enough!