SpiderOakのFAQ より。
If you are executing SpiderOak from the command line, this can be arranged by setting the Environment variable SPIDEROAK_HTTP_PROXY using this format:
http://proxy_hostname/
If your proxy server requires authentication, you may specify it this way:
http://username:password@proxy_hostname/
Windows版でも、この環境変数SPIDEROAK_HTTP_PROXY
は有効。