The only thing I could think of doing is to include a footer file with each page. Unfortunately that brings up your problem of 100 or so pages to update.
My advice to you is if you're using PHP, to rethink the structure of the site, and include the footer file. You should centralize the site so that all files that look the same, but have different content, use the same "template" and then you only have to update content not pages.
But it's just a suggestion. To add a few lines from the .htaccess is not possible, I think.
~Brett