Assuming a keychain already exists.
gpg --expert --edit-key KEYID
addkey
and go through process
quit
and save
gpg --output my_public_key.pub --export-ssh-key SUBKEYID!
(including the !)
gpg --list-keys --with-keygrip
to get the keygrip
Add keygrip to the sshcontrol
file under the $GNUPGHOME