WCF Rest service unknown property type list

I'm using a REST service that always returns an object of type ServiceResult. The cool thing about WCF is that the xml d开发者_高级运维eserialization is done automatically. Below are two example operation contracts:

[ServiceContract]
[XmlSerializerFormat]
public interface IMyService
{
    [OperationContract]
    [WebGet(
        BodyStyle = WebMessageBodyStyle.Bare,
        ResponseFormat = WebMessageFormat.Xml,
        UriTemplate = "authenticate?api={apiKey}&userName={userName}&password={password}")]
    ServiceResult Authenticate(string apiKey, string userName, string password);

    [OperationContract]
    [WebGet(
        BodyStyle = WebMessageBodyStyle.Bare,
        ResponseFormat = WebMessageFormat.Xml,
        UriTemplate = "getSchedules?api={apiKey}&user={userAccessCode}&states={states}&types={types}&filter={filter}")]
    ServiceResult GetSchedules(string apiKey, string userAccessCode, string states, string types, string filter);

}

The ServiceResult object contains two elements: State a simple string and Result, which is an object (so it can be anything). If i use object as its type, after deserialization I end up with a list of XmlNodes. So I created an abstract class Result that acts a a superclass for all the expected types:

[Serializable()]
[XmlRoot("ServiceResult", Namespace = "http://schemas.datacontract.org/2004/07/DTOModel.OpenApi")]
public class ServiceResult
{
    [XmlElement("Result")]
    public Result Result { get; set; }
    [XmlElement("State")]
    public string State { get; set; }
}

...

[XmlInclude(typeof(UserDto)), XmlInclude(typeof(ScheduleDto))]
[XmlType(Namespace = "http://schemas.datacontract.org/2004/07/DTOModel.Management")]
public abstract class Result
{
}

This works great an I can cast the superclass to the correct subclass after deserialization. But here's my problem: the result can also be an array and I cannot create a class (using CollectionDataContract) that inherits from Result and is an array (or list for that matter)...

Is there a solution or am I looking at this all wrong?

Thanks