six cgi calls seems a little over the top for a counter. Any tag which results in a call back to the server will do. Iframes and layers are a bit picky, but how about:

and have the perl script check the referer and return a simple javascript? You could use it to change the .src of six images that already existed, or perhaps just document.write('123456'); would suffice.

nb. remember it would be:

and not the usual text/html.