To customize the response to the browser, you will need to
capture the output from the cgi script. For cgi scripts at
another machine, your Apache handler will in affect act as a forward proxy to
the request: it will send the request with LWP::UserAgent and capture
the output with LWP::Response.
There is no difficulty if you know the Apache API.
Just ensure sure that all incoming and outgoing headers are copied,
especially the HTTP headers that may appear twice, like Cookie --
you cannot use functions like $r->headers_in that
return hash structures, thus suppressing the second Cookie header.