How Do I Write An OUTER APPLY Without A Table Function?

I'd like to select the last unshipped order, or if none is open, the last shipped order, for each customer. I noticed that all the examples on line for OUTER APPLY involve table-valued functions, but I have read (in a book I don't have here) that a subquery can work. The following shows what I want, but it isn't valid syntax:
SELECT c.CustomerName, oa.OrderNumber, oa.Status
  FROM Customers c
  OUTER APPLY (
    SELECT TOP 1 CustomerID, OrderNumber,
    CASE WHEN ShipDate IS NULL
         THEN 'due ' + CAST(DueDate AS VARCHAR)
         ELSE 'shipped ' + CAST(ShipDate AS VARCHAR)
         END AS Status,
    CASE WHEN ShipDate IS NULL
         THEN DueDate + 1000 -- Give open orders priority.
         ELSE ShipDate
         END AS SortOrder
    ORDER BY SortOrder
              ) AS oa ON oa.CustomerID = c.CustomerID