I do not know of any easy way. You may want to look through the string functions for php here - http://www.php.net/manual/en/ref.strings.php - and see if one of those would work for you and then you can just write a plugin to run it on the page text prior to spitting it out.

Or.... how about banning these users? Or setting it up so the first couple of posts must be approved? Or putting them on global ignore?