I decided to use Yandex Speller since at the time I was researching this issue it was clear that Google Spell was an undocumented and unsupported feature. http://api.yandex.ru/speller/

According to the TinyMCE, you can use aspell. http://www.tinymce.com/wiki.php/Plugin:spellchecker

You can get a windows build of aspell at http://aspell.net/win32/

Instructions are on the wiki on how to wire it up.