WIBNI if it were possible to delay the moment of signing messages?

As it is, if I write a message marked as <\#secure method=pgpmime
mode=sign>, Gnus tries to sign it right after I press C-c C-c. This is
probably fine for most people, but some of us are paranoid and keep
their secret key on a USB clipdrive, which gets attached only sometimes,
for a short period of time.

What I'd like to do is queue up all messages that are to be signed and
sign them all in one swell foop, when I'm ready to do it. This would
probably also allow people to stop caching their passprase in Emacs.

I thought just unplugging Gnus would do the trick, but it doesn't --
Gnus still insists that the message be signed before it gets placed into
the queue.

--J.