Все уже решено.
www.squid-cache.org
Цитирую:
How do I configure Squid forward all requests to another proxy?
Note: The information here is current for version 2.2.
First, you need to give Squid a parent cache. Second, you need to tell Squid it can not connect directly to origin servers. This is done with three configuration file lines:
cache_peer parentcache.foo.com parent 3128 0 no-query default
acl all src 0.0.0.0/0.0.0.0
never_direct allow all
^^^^^^^^^^^^^^^^^^^^^^
Тут были зарыты все грабли :)
Всем спасибо за внимание.