SqlKata: SELECT STUFF

Question

I have a stored procedure in SQL Server and I would like to transfer it to C# code using sqlKata.

I was able to do most of the transcripts but I am having trouble with one fragment.

It is my SQL Server stored procedure:

ALTER PROCEDURE [dbo].[my_procedure] 
    @UserId INT = 0
AS
BEGIN
    SELECT 
        STUFF((SELECT InboxHtml AS [text()]
               FROM [dbo].[my_procedure] WITH (NOLOCK)
               WHERE UserId = @UserId
                 AND DATEDIFF(DAY, GETDATE(), VisibleUntil) > 0
               FOR XML PATH(''), TYPE).value('text()[1]', 'nvarchar(max)'), 1, 0, NULL) AS InboxHtml 
END

And in C# with sqlkata:

db.Query("my_procedure").Select("InboxHtml").Where(new { UserId = id })
                .WhereRaw("DATEDIFF(DAY, GETDATE(), VisibleUntil) > ?", 0)

How can I add STUFF ... FOR XML PATH with sqlKata??

Thanks ! :)