if the proxy is an intermediary between the client and the requested url
could that url be sent to two different clients in response?
so in stead of this

[client]<-->[proxy]<-->[website]

it would be this

[client1]<-->[proxy]<-->[website]
.................. /
...........[client2]

meaning if [client1] requests "google.com" on the proxy server
the proxy server will request "google.com" and send it back to [client1]
as well as [client2]

it would just be url sharing between two people, like a real time delicious.com