Download ​Dojo (kitchen sink) and save it as /media/dojo/...

Save the following script as AddRichTextEditing.js into /media/js/admin/

document.write('<script type="text/javascript" src="/media/dojo/dojo.js"></script>');
document.write('<script type="text/javascript">dojo.require("dojo.widget.Editor2");</script>');

var AddEditor = {
	init: function() {
		var helptext = document.getElementsByTagName('p');
		for (var i = 0, ht; ht = helptext[i]; i++) {
				if (ht.firstChild.data == "Rich Text Editing.") {
				    ht.previousSibling.previousSibling.setAttribute("dojoType", "Editor2");
				}
		}
	},
}

addEvent(window, 'load', AddEditor.init);

This script looks for the help text "Rich Text Editing." and replaces the textarea before with the Dojo-Editor.

Define your model like this:

body = models.TextField('Body', help_text='Rich Text Editing.', blank=True, null=True)
...
class Admin:
     js = ['js/admin/AddRichTextEditing.js']

that´s it.

result could look like

​Screenshot (Preview)