有没有办法在 protobuf-net 代理类中定义替代转换函数(从/到接口)

使用 protobuf-net v2 build 668，我正在尝试序列化/反序列化一个类，该类包含一个定义为接口的成员，同时进行即时转换。通常，代理方法可以正常工作，但由于 C# 不允许对接口进行用户定义的转换，因此我无法定义转换。

谢谢

namespace ProtoBufNetTest
{
    using System.Diagnostics;
    using System.IO;
    using ProtoBuf;
    using ProtoBuf.Meta;
    class Program
    {
        static void Main()
        {
            RuntimeTypeModel.Default.Add(typeof(IDummy), false)
                .SetSurrogate(typeof(DummySurrogate));
            var container = new Container { Data = new Dummy { Positive = 3 } };
            using (var file = File.Create("test.bin"))
            {
                Serializer.Serialize(file, container);
            }
            using (var file = File.OpenRead("test.bin"))
            {
                container = Serializer.Deserialize<Container>(file);
                Debug.Assert(container.Data.Positive == 3);
            }
       }
    }
    // Outside of the project, cannot be changed
    public interface IDummy
    {
        int Positive { get; set; }
    }
    [ProtoContract]
    public class Container
    {
        [ProtoMember(1)]
        public IDummy Data { get; set; }
    }
    public class Dummy : IDummy
    {
        public int Positive { get; set; }
    }
    [ProtoContract]
    class DummySurrogate
    {
        [ProtoMember(1)]
        public int Negative { get; set; }
        // Does not compile : user-defined conversions to or from an interface are not allowed
        public static explicit operator IDummy(DummySurrogate value)
        {
            return value == null ? null : new Dummy { Positive = -value.Negative };
        }
        // Does not compile : user-defined conversions to or from an interface are not allowed
        public static explicit operator DummySurrogate(IDummy value)
        {
            return value == null ? null : new DummySurrogate { Negative = -value.Positive };
        }
        // Fake attribute, does not exist but could work if it did
        [ProtoConvertFrom]
        public static IDummy From(DummySurrogate value)
        {
            return value == null ? null : new Dummy { Positive = -value.Negative };
        }
        // Fake attribute, does not exist but could work if it did
        [ProtoConvertTo]
        public static DummySurrogate To(IDummy value)
        {
            return value == null ? null : new DummySurrogate { Negative = -value.Positive };
        }
    }
}

[ProtoContract]
class DummySurrogate
{
    [ProtoMember(1)]
    public int Negative { get; set; }
    [ProtoConverter]
    public static IDummy From(DummySurrogate value)
    {
        return value == null ? null : new Dummy { Positive = -value.Negative };
    }
    [ProtoConverter]
    public static DummySurrogate To(IDummy value)
    {
        return value == null ? null : new DummySurrogate
           { Negative = -value.Positive };
    }
}