Hello JRM,
In case the proxy is used for the Internet connection, the following system environment variable should be set up (for the current build 3149):
HTTP_PROXY=hostname:port
The properties of the proxy in Windows can be checked in Control Panel -> Network and Internet -> Internet Options -> Connections -> LAN Settings -> "Use a proxy server for your LAN".
In case the proxy is requiring the autentification, then additional variable should be used:
HTTP_PROXY_CREDENTIALS=user:password
After setting up these variables it is recommended to reboot and re-run PhotoScan.
As for offline activation, usually it doesn't require administrator privileges, providing that current used has access write rights to Program Data folder and activation request file is not saved to the system folder that requires special permissions.