Don't worry. I worked out how to activate the built-in TinyMCE plugin:
On the "General Settings" page of the TinyMCE HTML Editor section of the Plugins menu, I added
,wrap,restoredraft
at the end of the first line in the Editor toolbar box. Then I put
{"plugins" : "lists,table,style,layer,advhr,advlink,emotions,inlinepopups,searchreplace,paste,directionality,fullscreen,nonbreaking,contextmenu,insertdatetime,save,iespell,preview,print,noneditable,visualchars,xhtmlxtras,template,pagebreak,autosave"}in the Custom Configuration box.
After purging all caches, the new button appears at the end of the first row.