Maybe you could take Apache out of the picture entirely (for testing purposes) and run a simple Perl webserver, such as HTTP::Server::Simple. Then you could essentially send anything you want, without having to mess with Apache's standard request cycle...

But, as Corion said, it's a little hard to be more specific, without knowing what exactly you need to do.  In other words, if Apache is a constituent to be included in the testing, this won't work of course.