Sorting GridView With ASC/DESC When Using Stored Procedure???

I have a stored procedure in my SQL 2005 Server database named Foo that accepts two parameters, @paramA and @paramB.

In my ASP.NET page, I have these:

<asp:GridView
    id="gv"
    runat="server"
    AutoGenerateColumns="true"
    DataSourceID="DS"
    AllowSorting="true"
    DataKeyNames="ID"
/>

<asp:SqlDataSource
    ID="DS"
    runat="server"
    ConnectionString="<%$ ConnectionStrings:CS1 %>"
    SelectCommand="Foo"
    SelectCommandType="StoredProcedure"
    OnSelecting="DS_Selecting"
>
    <asp:Parameter Name="paramA" Type="String" />
    <asp:Parameter Name="paramB" Type="String" />
</asp:SqlDataSource>

In my setup, paramA and paramB are set in DS_Selecting(), where I can access the Command.Parameters[] of DS.

Now, here's the problem. As you can see, the GridView allows for sorting. When you click on a header title to sort, however, the GridView becomes empty. My question is, how can I get the GV sorted and in the correct direction (i.e. asc/desc)?

My first step in my attempt was to add another parameter to the SqlDataSource and sotred procedure Foo (e.g. @SortByColumn), then changed Foo appropriately:

    ALTER PROCEDURE Foo
        @paramA nvarchar(64),
        @paramB nvarchar(64),
        @SortColumn nvarchar(16) = 'SearchCount'
    AS
        SELECT * FROM Searches ORDER BY
            CASE
                WHEN @SortColumn='SearchCount' THEN SearchCount
                WHEN @SortColumn='PartnerName' THEN PartnerName
                ELSE ID
            END

That works find and dandy. But wait--I want to get the correct ORDER BY direction too! So I add another parameter to the SqlDataSource and Foo (@SortDirection), then alter Foo:

    ...
        SELECT * From Searchces ORDER BY
            CASE
                /* Keep in mind that CASE short-circuits */
                WHEN @SortColumn='SearchCount' AND @SortDirection='desc' SearchCount DESC
                WHEN @SortColumn='SearchCount' SearchCount
                WHEN @SortColumn='PartnerName' AND @SortDirection='desc' PartnerName DESC
                WHEN @SortColumn='PartnerName' PartnerName
                WHEN @SortColumn='ID' AND @SortDirection='desc' ID DESC
                ELSE ID
            END
    ...

But including DESC or ASC after the column name to sort by causes SQL to error.

What the heck can I do, besides convert all my stored procedures into in-line statements inside the ASP page, where I could then dynamically construct the appropriate SQL statement? I'm really at a loss on this one! Any help would be much appreciated!

Am I missing a much simpler solution? I am making this too complicated?