"Hidden" authorize to squid as parent proxy ?

Any suggestions how to “secretly” authorize a MT-box, running web-proxy, to a parent squid on a LINUX machine ?
The MT-box is (also) running hot-spot, as a transparent/web proxy, and I want to use squid-caching for the hotspot users, but there should be no need for the users to explicitly authorize to squid. Otherwise, I want to serve the MT-hotspot users ONLY thru a special instance of squid.