Hello.
I know that this subject is very old now, but if you still need it...
you can create your own toolbar and add the class you want on the buttons. a bit like this :
<div class="btn-toolbar">
<div class="btn-group">
<button type="button" class="btn btn" onclick="return Joomla.submitform('TASK.cancel');">
<span class="icon-cancel"></span><?php echo JText::_('COMPONENT_JTOOLBAR_CANCEL') ?>
</button>
</div>
<div class="btn-group">
<button type="button" class="btn btn-success" id="buttonSave" onclick="Joomla.submitbutton('TASK.save')">
<?php echo JText::_('COMPONENT_JTOOLBAR_SAVE') ?> <i class="icon-arrow-right"></i>
</button>
</div>
</div>
