Creating a custom UIAutomation property in c#

Question

I'm currently adding UIA support to a pane control and child control by implementing IRawElementProviderFragmentRoot and IRawElementProviderFragment respectively.

UIA fragments use the method public object GetPropertyValue(int propertyId) to return a specific property to a test recorder such as Ranorex or Test Complete. For example:

/// <summary>
/// Retrieves the value of a property supported by the UI Automation provider.
/// </summary>
/// <param name="propertyId"></param>
/// <returns></returns>
public object GetPropertyValue(int propertyId)
{
    if (propertyId == AutomationElementIdentifiers.NameProperty.Id)
    {
        // Name of this control. Since this is a top level pane, we'll use the partition name
        return View.Document.FullName;
    }
    else if (propertyId == AutomationElementIdentifiers.ControlTypeProperty.Id)
    {
        // Pane controls represent a level of grouping lower than windows or documents, but above individual controls.
        // The user can navigate between panes and within contents of the current pane, but cannot navigate between items in 
        // different panes. The pane navigation shortcut is typically CTRL + TAB.
        return ControlType.Pane.Id;
    }
    else if (propertyId == AutomationElementIdentifiers.IsContentElementProperty.Id)
    {
        // Indicates whether the element contains content that is valuable to the end user
        return true;
    }
    else if (propertyId == AutomationElementIdentifiers.IsControlElementProperty.Id)
    {
        // Indicates whether the element is viewed as a control
        return true;
    }
    else if (propertyId == AutomationElementIdentifiers.IsKeyboardFocusableProperty.Id)
    {
        // You can't explicitly focus a tab, the whole window gets focused
        return false;
    }
    else
    {
        // Null indicates no support
        return null;
    }
}

I wish to register a custom property and handle the Get call in the method above. According to this MSDN article, your custom property can return

1. UIAutomationType_Bool
2. UIAutomationType_Double
3. UIAutomationType_Element
4. UIAutomationType_Int
5. UIAutomationType_Point
6. UIAutomationType_String

which is exactly what I want. Unfortunately, the instructions are in C++ and there doesn't seem to be a corresponding C# assembly to do all this. Will I have to do some managed->unmanaged marshaling to achieve this? How would I go about it?

Thanks in advance!