function YOURTHEME_widont($str = '') { 
$str = rtrim($str); 
$space = strrpos($str, ' '); 
if ($space !== false) { 
  $str = substr($str, 0, $space).' '.substr($str, $space + 1);
 } 
return $str; 
}

http://club-sandru.ro/blog/solving_the_widow_problem_on_your_drupal_website.html

Anywhere, the variable $title is printed in a template file, it can be wrapped in this function:

YOURTHEME_widont($title)

Solving the widow problem on your Drupal website Titles

PHP