Yes, it is possible.
The easiest way would be to set up a proxy server on one PC, and tell your internet browser, IM programs etc to use the proxy server on the other PC with the 3G connection.
AnalogX Proxy is simple and works, but other may recommend other stuff.
It's also possible to set up other stuff, but going any more complicated is likely to interfere with your network access at respawn unless you know what you're doing.