Delaying Calling JQuery or javascript method from c#

I've got a mixture of JQuery and Ajax partial postbacks on a webforms page and I'm trying to stop the user navigating away from a page without their changes having been saved.

It's working pretty well unless one of the data validators on the page is invalid. There is a jquery method on the submit button that basically nulls the onbeforeunload event. In the event that the validators are invalid, I dont want that to happen, so I turned off the client side validation, and in the method, called Page.Validate(), then if the page was invalid, I tried to register a startup script as described here to reset like so:

if (!Page.IsValid) {
            ScriptManager.RegisterStartupScript(this, this.GetType(), "", "setConfirmUnload(true);", true);
            return;
        }

If I run the click submit and the page is invalid, the call to setConfirmUnload(true) happens, but the method cant be found (presumably because I re-set this up every time a postback happens?

The actual error is " JavaScript runtime error: 'setConfirmUnload' is undefined", possibly because the bindEvents() hasnt yet re-run and therefore created it?

I thnk my problem stems from the fact that I am using partial postbacks and autopostbacks, setting up data as the user modifies the form. By default that blitzes my jquery, so I rebind the jquery calls on document.ready() as well as on postback using

<script type="text/javascript">
        // attach the event binding function to every partial update
        Sys.WebForms.PageRequestManager.getInstance().add_endRequest(function (evt, args) {
            bindEvents();
        });
    </script>

And my Bind Events method looks like:

 function bindEvents() {

        // stuff removed for brevity here...


        $(function () {
            // Prevent accidental navigation away
            $(':input, select').bind(
                'change', function () { setConfirmUnload(true); });

            $('.noprompt-required').click(
                function () { setConfirmUnload(false); });

            function setConfirmUnload(on) {
                window.onbeforeunload = on ? unloadMessage : null;
            }
            function unloadMessage() {
                return ('You have entered new data on this page. ' +
                        'If you navigate away from this page without ' +
                        'first saving your data, the changes will be lost.');
            }

            window.onerror = UnspecifiedErrorHandler;
            function UnspecifiedErrorHandler() {
                return true;
            }

        });

    }        

If that's the case, is there a way I can force the script to run after the bindEvents() call has happened?