I was able to achieve something similar to this by redirecting the requests
through a custom local proxy. The proxy could look at the path of the GET
requests and reply with 304 'Not Modified' to all paths that you are NOT
interested in updating, while forwarding the remaining requests to the
server.

Take a look at Twisted web framework and particularly the example here [1].
Also, if you need to talk to the server through another (remote) proxy, you
can do it using ProxyAgent class [2] from the the local proxy.

[1] <http://stackoverflow.com/a/9469400>
[2] <http://twistedmatrix.com/documents/current/web/howto/client.html>