[squid-users] transparent proxy by URL?

Hi all,
I've a transparent proxy using iptables+squid. It's possible to
instruct squid to proxy only if the URL does not contain a given
string?

For example, if you try to access to
http://lol.example.com/ALLOWEDSTRING/page.html through squid, it
should allow direct access.

Anyone have a setup like this?

Many thanks!

--
Jordi
PS: Yes! the allowed string will be "proxytest" ;)