I would like to share a single OpenID within multiple persons, but in a nice safe way (password sharing does not count as safe), exactly like you can share a single Twitter account with CoTweet. Does anyone know an OpenID provider (or relay) that would provide such a feature?
You could use an openid provider that uses a client-side SSL certificate for authentication such as myopenid.com, and then make sure all the people that need to use the openid have the certificate.
If you delegate an OpenID to a shared website (e.g. a blog on blogger), each person who can log in to this website should be able to use it.
E.g. I use http://www.raphink.info as my OpenID, and raphink.info is where I have my blogspot blog. I assume if I allowed other people as editors for this blog, they could share the OpenID.