A página de manual que vejo diz que isso só funciona com http / https. A menos que você tenha encontrado um patch ou algo que eu não esteja ciente?
Homem OpenVPN
--port-share
When run in TCP server mode, share the OpenVPN port with another application, such as an HTTPS server. If OpenVPN senses a connection to its port which is using a non-OpenVPN protocol, it will proxy the connection to the server at host:port. Currently only designed to work with HTTP/HTTPS, though it would be theoretically possible to extend to other protocols such as ssh.
Not implemented on Windows.