I think what they want to do is temporarily grant someone else the ability to authenticate using their passpack account, without actually exposing the passwords

I think what they want to do is temporarily grant someone else the ability to authenticate using their passpack account, without actually exposing the passwords. This is, of course, not possible in the general case. You can (sort of) do it for a specific site by changing the password and changing it back when you're done, which is what I ask people to do whenever they want me to poke around in their accounts. That obviously doesn't generalize across sites.