Add placeholders when necessary and make them act like placeholders. Use CSS to style .placeholder

jquery.placeholders.js

if  ( ! Modernizr.placeholder ) {
  (function($) {
    $(document).find('input[placeholder]').each(function() {
      var el = $(this).on('keyup blur change', function() {
        placeholder[this.value.length > 0 ? 'hide' : 'show']();
      });
      var css = {};
      var offset = el.position();
      css.left = offset.left + parseFloat(el.css('padding-left')) + parseFloat(el.css('margin-left'));
      css.top = offset.top + parseFloat(el.css('padding-top')) + parseFloat(el.css('margin-top'));
      var placeholder = $('<span class=placeholder>' + el.attr('placeholder') + '</span>').insertAfter(el).css(css).on('click', function() {
        el.trigger('focus');
      });
      setTimeout(function() {
        el.trigger('blur');
      }, 13);
    });
  })(jQuery);
}