Insert a new button to a form created with the gem "bootstrap-wysihtml5-rails" and manipulate it with bootbox.js https://github.com/jhollingworth/bootstrap-wysihtml5 http://bootboxjs.com

gistfile1.html

<script type="text/javascript">
  $('#post_content').each(function(i, elem) {
    $(elem).wysihtml5();
    $(".wysihtml5-toolbar").append('<li id="target"><a class="btn" title="Insert gallery" tabindex="-1" href="javascript:;" unselectable="on"><i class="icon-th-large"></i></a></li>');

      $("#target").click(function() {
        bootbox.alert("Hello world!");
      });
  });
</script>