Conditional Views

I have a view which has to be versatile enough to perform different calculations. For instance, using the view below I may want the stock level for that particular wine or in another instance I would the need the stock level for all wines that share the same type. Note that I would never need a combonation of both in the same view.

Is there anyway to specify <myVar> before or when calling this view?

CREATE VIEW vwWines
AS

SELECT
tblWine.ID,
tblWine.WineTypeID,
StockQty =
CASE
WHEN <myVar> = 1
THEN tblWine.StockQty
ELSE
(
SELECT
SUM(StockQty)
FROM
tblWine AS tblWineTwo
WHERE
tblWine.WineTypeID = tblWineTwo.WineTypeID
)
END
FROM
tblWine
Note: This view has been simplified and been done on the fly so may contain errors