Did you ever thought about the idea, that the browser can use AJAX to send changes in the text fields, checkboxes and so on to the server. So the server can check the actual data and retrieve or remove error messages. They would be displayed on the place which the JSP designer has planed.
The idea is, that the developer will not need to change the JSP files but only the logic (the action classes and perhaps the underlying Model, i.e. the EJB session beans).