Pretty sure you cannot do this using XML Auto.

Try Using XML Path

Here's an example using Path from AdventureWorks

SELECT

h.SalesOrderID,

h.OrderDate,

h.DueDate,

h.ShipDate,

h.Status,

h.SubTotal,

h.TaxAmt,

h.Freight,

h.TotalDue,

(SELECT

CarrierTrackingNumber,

OrderQty,

ProductID,

UnitPrice,

UnitPriceDiscount,

LineTotal,

ModifiedDate

FROM [Sales].[SalesOrderDetail] d

WHERE h.SalesOrderID = d.SalesOrderID

FOR XML PATH('OrderDetail'), ROOT('OrderDetails'), Type)

FROM [Sales].[SalesOrderHeader] h

WHERE h.SalesOrderID = 43666

FOR XML PATH('SalesOrder'), ROOT('SalesOrders')

<SalesOrders>

<SalesOrder>

<SalesOrderID>43666</SalesOrderID>

<OrderDate>2001-07-01T00:00:00</OrderDate>

<DueDate>2001-07-13T00:00:00</DueDate>

<ShipDate>2001-07-08T00:00:00</ShipDate>

<Status>5</Status>

<SubTotal>6079.6842</SubTotal>

<TaxAmt>486.3747</TaxAmt>

<Freight>151.9921</Freight>

<TotalDue>6718.0510</TotalDue>

<OrderDetails>

<OrderDetail>

<CarrierTrackingNumber>D46A-40CA-8D</CarrierTrackingNumber>

<OrderQty>1</OrderQty>

<ProductID>764</ProductID>

<UnitPrice>419.4589</UnitPrice>

<UnitPriceDiscount>0.0000</UnitPriceDiscount>

<LineTotal>419.458900</LineTotal>

<ModifiedDate>2001-07-01T00:00:00</ModifiedDate>

</OrderDetail>

<OrderDetail>

<CarrierTrackingNumber>D46A-40CA-8D</CarrierTrackingNumber>

<OrderQty>1</OrderQty>

<ProductID>753</ProductID>

<UnitPrice>2146.9620</UnitPrice>

<UnitPriceDiscount>0.0000</UnitPriceDiscount>

<LineTotal>2146.962000</LineTotal>

<ModifiedDate>2001-07-01T00:00:00</ModifiedDate>

</OrderDetail>

</OrderDetails>

</SalesOrder>

</SalesOrders>