class ButtonAdmin(admin.ModelAdmin):
    """
    A subclass of this admin will let you add buttons (like history) in the
    change view of an entry.

    ex.
    class FooAdmin(ButtonAdmin):
       ...

       def bar(self, request, obj=None):
          if obj != None: obj.bar()
          return None # Redirect or Response or None
       bar.short_description='Example button'

       list_buttons = [ bar ]
       change_buttons = [ bar ]

    you can then put the following in your admin/change_form.html template:

       {% block object-tools %}
           {% if change %}{% if not is_popup %}
           <ul class="object-tools">
           {% for button in buttons %}
             <li><a href="{{ button.func_name }}/">{{ button.short_description }}</a></li>
           {% endfor %}
           <li><a href="history/" class="historylink">History</a></li>
           {% if has_absolute_url %}<li><a href="../../../r/{{ content_type_id }}/{{ object_id }}/" class="viewsitelink">View on site</a></li>{% endif%}
           </ul>
           {% endif %}{% endif %}
       {% endblock %}

    """
    change_buttons=[]
    list_buttons=[]

    def button_view_dispatcher(self, request, url):
        # Dispatch the url to a function call
        if url is not None:
            import re
            res = re.match('(.*/)?(?P<id>\d+)/(?P<command>.*)', url)
            if res:
                if res.group('command') in [b.func_name for b in self.change_buttons]:
                    obj = self.model._default_manager.get(pk=res.group('id'))
                    response = getattr(self, res.group('command'))(request, obj)
                    if response is None:
                        from django.http import HttpResponseRedirect
                        return HttpResponseRedirect(request.META['HTTP_REFERER'])
                    return response
            else:
                res = re.match('(.*/)?(?P<command>.*)', url)
                if res:
                    if res.group('command') in [b.func_name for b in self.list_buttons]:
                        response = getattr(self, res.group('command'))(request)
                        if response is None:
                            from django.http import HttpResponseRedirect
                            return HttpResponseRedirect(request.META['HTTP_REFERER'])
                        return response
        # Delegate to the appropriate method, based on the URL.
        from django.contrib.admin.util import unquote
        if url is None:
            return self.changelist_view(request)
        elif url == "add":
            return self.add_view(request)
        elif url.endswith('/history'):
            return self.history_view(request, unquote(url[:-8]))
        elif url.endswith('/delete'):
            return self.delete_view(request, unquote(url[:-7]))
        else:
            return self.change_view(request, unquote(url))

    def get_urls(self):
        from django.conf.urls.defaults import url, patterns
        from django.utils.functional import update_wrapper
        # Define a wrapper view
        def wrap(view):
            def wrapper(*args, **kwargs):
                return self.admin_site.admin_view(view)(*args, **kwargs)
            return update_wrapper(wrapper, view)
        #  Add the custom button url
        urlpatterns = patterns('',
            url(r'^(.+)/$', wrap(self.button_view_dispatcher),)
        )
        return urlpatterns + super(ButtonAdmin, self).get_urls()

    def change_view(self, request, object_id, form_url='', extra_context=None):
        if not extra_context: extra_context = {}
        if hasattr(self, 'change_buttons'):
            extra_context['buttons'] = self._convert_buttons(self.change_buttons)
        if '/' in object_id:
            object_id = object_id[:object_id.find('/')]
        return super(ButtonAdmin, self).change_view(request, object_id, form_url, extra_context)

    def changelist_view(self, request, extra_context=None):
        if not extra_context: extra_context = {}
        if hasattr(self, 'list_buttons'):
            extra_context['buttons'] = self._convert_buttons(self.list_buttons)
        return super(ButtonAdmin, self).changelist_view(request, extra_context)

    def _convert_buttons(self, orig_buttons):
        buttons = []
        for b in orig_buttons:
            buttons.append({ 'func_name': b.func_name, 'short_description': b.short_description })
        return buttons