You can. Just take care of that you have to output CGI headers, not http headers. This means in practice that you do not have to print a http status line (the one with a three-digit number), instead the webserver will print one as approperiate (200 normally, 302 in case you print a Location header so the server thinks it's a redirect), and that the server will correct the line endings of your header to crlfs. (Update: the server will also do the chunked encoding if you don't specify the Content-length, do the keepalive connection, and lots of other magical stuff I can't even imagine.)

The only header you are required to print is Content-type. Just search perlmonks for "Content-type", and you'll find lots of examples. (In case you wanted to write http requests by hand, you can do that too: in that case the only required header is Host.)

Update: it seems I didn't answer your question. Well, the CGI module does not output any headers, so it is safe to use it just the input part.