Userlevel IP Masquerading

Is there any way to do a user level IP Masquerading?

Explanation:

I have a machine with 202 address (directly connected to net). I want to
access internet from another machine which has only an internal address. I am
able to setup IP Masquerading but I want to allow only some users access to the
machine. Some search on this topic lead me to socks server, but I donot want
to use it as the application I have does not support for proxies. In essence,
is it possible to setup the system so that,

myname$ telnet google.com 80
Trying 216.239.39.99...
Connected to google.com.
Escape character is '^]'.


but for other users,

someoneelse$ telnet google.com 80
gets struck.

-- M Rajsekar