hi to everybody

at first excuse me about my english and plz write ur answers by sipmle word!
I am a admin of a ISP in iran. in iran most of the sites filtered by data communication center and we don't have permision to use internet via sat so I have a question:
can I configure my cache (ISA or Squid)to use proxy for some web sites (not for all).
and my users don't set anything on their systems!

this is my mail: [email]amm**56@**********[/email]
plz help me!