IL2CPP issue: Sgen.exe with xsi:type = Inherited types cannot be parsed by XmlSerializer

I have built a very simple test project below, to illustrate a bug I'm running into when using IL2CPP and xsi:type with sgen.exe pre-compiled Xml Serializer.
Any ideas/suggestions on how to fix this would be greatly appreciated.

I have this very simple XML:

Code (CSharp):

1. <Engine xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
2.     <Child xsi:type="MyType" />
3. </Engine>

Which follows this simple class structure:

Code (CSharp):

1. [Serializable]
2. public class Engine
3. {
4.     public BaseType Child;
5. }
6.  
7. public class BaseType { }
8. public class MyType : BaseType { }

To speed up loading, we use sgen.exe, to generate the pre-compiled XmlSerializer.dll and place it in the project Plugins folder.
The following command then calls the pre-compiled XmlSerializer to create the Engine object:

Code (CSharp):

1. new Microsoft.Xml.Serialization.GeneratedAssembly.EngineSerializer().Deserialize(xml);

I can then use the XML above, with xsi:type to load the inherited "MyType".
And this all works fine in Mono! But as soon as I switch to IL2CPP (using .NET 4.0) I get the following error.
It seems like the IL2CPP stripping process is somehow removing the type, but I've even tried using

link.xml

to force include the full XmlSerializer.dll.

Code (CSharp):

1. InvalidOperationException: The specified type was not recognized: name='MyType' namespace='', at <Child xmlns=''>
2.   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReader1.Read2_BaseType (System.Boolean isNullable, System.Boolean checkType) [0x00000] in <00000000000000000000000000000000>:0
3.   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReader1.Read3_Engine (System.Boolean isNullable, System.Boolean checkType) [0x00000] in <00000000000000000000000000000000>:0
4.   at Microsoft.Xml.Serialization.GeneratedAssembly.EngineSerializer.Deserialize (System.Xml.Serialization.XmlSerializationReader reader) [0x00000] in <00000000000000000000000000000000>:0
5.   at System.Xml.Serialization.XmlSerializer.Deserialize (System.IO.Stream stream) [0x00000] in <00000000000000000000000000000000>:0
6.   at SerializerTest.Start () [0x00000] in <00000000000000000000000000000000>:0
7.  
8. (Filename: currently not available on il2cpp Line: -1)

Any ideas/suggestions on how to fix this?
I've attached the small sample project as well.