I don't know if there is a direct way to do this, but you could always emulate the browser's confirmation box yourself. Here's a simple function I cooked up based on the specs at MSDN:

function triggerBeforeUnload() {

  var event = {};

  handler(event);



  if (typeof event.returnValue == 'undefined' ||

      confirm('Are you sure you want to navigate away from this page?nn' + event.returnValue + 'nnPress OK to continue, or Cancel to stay on the current page.')) {

    // Continue with page unload

  } else {

    // Cancel page unload

  }

}

Edit: In jquery.formobserver.js, right after the definition of function beforeunload(e) { ... }, add this line:

handler = beforeunload;

Note the change in the original code: window.onbeforeunload has been replaced by handler.