Proxy config

[Richard Barry]

Is there any way to use "export http_proxy" and specify a range of addresses
to not use the proxy for (like the "No Proxy for" field in Firefox)?  I'm
behind a firewall and all network apps have to go through the proxy for IPs
outside our network, but not for IPs inside the network (we pay for going
through the proxy).  I can set Firefox up like that, but how do I do it for
other network apps (like apt) where "export
http_proxy=http://username:password@host:port" would usually work?  

Richard