Custom User Directory with no login form

I’ve added a custom user directory component, which works fine.
However, I’d like to not have a login form for that. Meaning: I do not want a manual login mechanism available for this user directory. Unfortunately, this seems not possible, as I have to implement the getLoginForm method in my customUD.cfc as well as I seem to need to have a displayLogin handlers in webskin/customLogin.

Is there any chance to define the custom UD in a way that it won’t need a login form?

Background: for this user group, a single sign-on is implemented. Users won’t get access to webtop, but pages on the frontend need to be populated with data from a third-party db, so I need to know the session context for the user, thus the custom UD.

Let me know whether there is some kind of config/switch to disable form-based login for custom UD.