is there a way to modify the date when signing?

[Anonymous Remailer (austria)]

Hello,

Is there a way to make a signature cleartext or detached, with the date
modified, erased, or otherwise different then system date?

I would like to sign all my messages and have it appear to be signed on
the Epoch date 1970...unless there is some other default way gnupg 
handles signing date masking.

Thanks