need to convert QueryStringParameter from string to int64

I have a gridview that is bound to a objectdatasource(ods).  It uses this:
        <SelectParameters>
            <asp:QueryStringParameter Name="customerID" QueryStringField="ID"  Type="String" />
        </SelectParameters>

But here is the deal...the SelectMethod needs customerID to be an integer64 instead of a string.
After researching, I found that I need to do the conversion in the Selecting event of the ods.

So I added this line, but this isn't working because customerID remains as string after this line is executed:
Convert.ChangeType(e.InputParameters("customerID"), TypeCode.Int64)

Can someone please tell me what I need to do to change the datatype of the SelectParameter from string to int64?  Thank you!