Bitcore Wallet Service with a cold storage


In the BWS guide it is written that one can run an own Bitcore Node as a backend for a Copay wallet client. While the Copay app is really great, it is missing the support for cold storage, which would be an ultimate security measure. Is it already possible or technically possible through a minor extension of the existing setup to have a manual process of signing outgoing transactions with a private key on a cold storage?