#agent-forwarding and sudo
[http://serverfault.com/questions/107187/ssh-agent-forwarding-and-sudo-to-another-user]
As you mentioned, the environment variables are removed by sudo, for security reasons.
But fortunately sudo is quite configurable: you can tell it precisely which environment variables you want to keep thanks to the env_keep configuration option in /etc/sudoers.
For agent forwarding, you need to keep the SSH_AUTH_SOCK environment variable. To do so, simply edit your /etc/sudoers configuration file (always using visudo) and set the env_keep option to the appropriate users. If you want this option to be set for all users, use the Defaults line like this: