Before you get too excited with dreams of easy money, I've already tried the .htaccess method of prepending and the mod_layout method. Both methods throw errors about headers already sent, or session start problems.
The problem is with prepending html or php files to things like phpBB, Mambo, Drupal, etc. I've looked high and low for a way to do this which does not cause errors, but to no avail. If anyone holds the secret, or thinks they can create something that will work, shoot me a PM. Thank you.