If you have SSH access to a computer on a remote network you can use SSH to create a SOCKS proxy over a tunnel between you and the remote host. You would then configure your browser to use your local host as the SOCKS proxy.
To set up a SOCKS proxy connection you will initiate an SSH connection from your local machine. The two best methods, depending on your local OS are to either use the
ssh command or PuTTy (for Windows). To use the ssh command, open a terminal and type:
ssh -D 8080 email@example.com
To use PuTTy, open PuTTy and specify the host to connect to, then expand the Connections branch on the left. Finally expand SSH and click Tunnels. In Source Port specify a port number greater than 1024 and select Add. If you'd like to save your connection you can go back to the Session branch, specify a name under Saved Sessions and click save, then click Open.
Most browsers allow you to specify a proxy server to route traffic through. In Internet Explorer go to Tools -> Internet Options and click the Connections Tab, then LAN Settings and configure the Proxy settings using localhost for the hostname and the port you chose above.
In FireFox the best add-on I've found for managing proxies is FoxyProxy. If this is just a one time thing though go to Tools -> Options -> Advanced. Click the Network tab and click the Settings button under Connection. Select the Manual Proxy Configuration radio button and fill in the information for your proxy, again using localhost for the hostname and the port you chose above. If you don't want to proxy all of your protocols you can leave them blank and they will route normally.