Adding “ ” before the last word in multiple defined areas with a plugin

How would this be done with javascript or a plugin? This would prevent widows from happening in my WordPress posts. Shaun Inman has created a similar plugin for post titles, but not for actual posts. Can his plugin be modified to include posts?

http://shauninman.com/archive/2006/08/22/widont_wordpress_plugin

Here is a screenshot of my post with a widow:

http://cl.ly/image/0A0j383H0Z2U

Drop in add_filter( 'the_content', 'widont' ); (and the same for the_excerpt if required).

This’ll apply the function to the post content in addition to the title (the_title).