Cisco IP Communicator no longer supports AutoUpdate functionality provided in any release of Cisco Unified Communications Manager. You must use a software deployment tool and the Cisco IP Communicator installer to update the application.
If you put the config file on a TFTP server locally on your PC it will registered just fine. The phone should try to register with the CCM pointed by TFTP setting normally. So if you have CCM running on PUB it should work despite the fact TFTP traffic is blocked.