I think this will be a feature request to add the alternate login methods to the sign in module.
But as a workaround, instead of using the sign in module, you can use an HTML instance with a link to
/Secure/Login.aspx?returnurl=/SecuredLandingPage.aspx
This way they will be able to use whatever sign in method they need, and once signed in they will be returned to the landing page.
Jamie