Sometimes you need to install an Eclipse plugin without an access to the Internet or -perhaps more frequently- with an (extremly stupid) firewall that blocks the traffic and prevents the download (and additionally destroys your productivity as developer by pretending all the technical subjects are related to hacking :p)
Unfortunately, the website for this plugin doesn’t offer a zip file in order to install it offline. And your network administrator -who doesn’t want to understand anything in development- has all the power (you’re completly out of luck, maybe you should consider another company rather than be reading this ).
So, here is what you can do in order to create a mirror of the update website, from another computer that has Eclipse installed and that has access to the net:
/eclipse -application org.eclipse.update.core.standaloneUpdate -command mirror -from http://www.aniceplugin.com/update-site -to /path/to/local/directory
The various commands for the update manager are further detailed in the Eclipse documentation under the section “Running update manager from command line”.