How do I set up ObjectDataSource select parameters at runtime

I'm trying to add parameters to an objectDataSource at runtime like this:

        Parameter objCustomerParameter = new Parameter("CustomerID", DbType.String, customerID);
        Parameter objGPDatabaseParameter = new Parameter("Database", DbType.String, gpDatabase);

        //set up object data source parameters
        objCustomer.SelectParameters["CustomerID"] = objCustomerParameter;
        objCustomer.SelectParameters["Database"] = objGPDatabaseParameter;

At what point in the objectDataSource lifecycle should these parameters be added (what event)? Also, some values are coming from a master page property (which loads after the page_load of the page containing the objectDataSource).