How to tell gpg not to start gpg-agent on a remote machines when using gpg agent forwarding

[Thomas Glanzmann]

Hello,
I'm using gpg using gpg agent forwarding over ssh on a remote system.
Sometimes my agent socket is not available. If I start any gpg
operation, it starts a new agent. Is there a configuration option that I
can specify so that gpg gives up is there is no socket or no agent
behind a socket instead of starting a new agent?

Cheers,
        Thomas