[Zope] modify 'Server' response header

Hi, is there a way to control the 'Server' response header in ZServer like it could be done with the ServerTokens directive in apache? In an apache -> squid -> zope configuration I tried apache's mod_headers but this only works if the page is cached in the browser (304 Not Modified), a browser-reload for example reveals ZServer. Does anyone know how to accomplish this without modifying any zope code? Thanks Jens