A similar question was asked on Stack Overflow back in January.
John Mueller was kind enough to respond with the following:
"googleon" and "googleoff" are only supported by the Google Search
Appliance (when you host your own search results, usually for your own
They are not supported by Google's web-search at all.
As far as I know there is no such way of telling Google not to index a element of the page, Google wants to take everything into consideration as there may be undiserables on the page. Hiding visible content from Google is know as Cloaking.