Checkout the InsertWord plugin for xinha. Xinha is one of the successors of htmlara, if you are lucky, this plugin works as well with htmlarea.
http://xinha.python-hosting.com/wiki/InsertWords
xinha is highly compatible to htmlarea 3, but has many bugs removed. It is committed to the oacs-5-2 branch. If you use xinha, you just have to enable the plugin... (see also xowiki thread)