Single Sign-On with Google Apps + App Engine

Is it possible to achieve SSO with the built-in OpenId on App Engine? I've been trying to integrate a Marketplace app and get the user logged in when coming from Google Apps (the admin panel or universal navigation). I failed miserably, then now I found this:

"The one exception to this is applications which do hybrid OpenID/OAuth — whitelisting does not currently work with this approach." (from here)

I assume that I have to implement OpenId using a library instead of using the built-in one to achieve SSO with Google Apps in my app? Or if it is possible with built-in OpenId, is there an example anywhere that shows how to do this?