Diggit Drupalextras

I'm using Open Atrium as an intranet for a small group planning a conference, and I also want to get them using Google Apps. One member expressed interest/concern about having too many logins for committee members to remember. Since Drupal implements OpenID support, and Google Apps is now and OpenID provider I figured I could offer that option for a single sign on. Problem is, Google Apps has a proprietary discovery mechanism. Google has provided some documentation, but it's not particularly clear to me on how to proceed. The solution could be very simple, and just something I'm missing. It might not even be necessary to use Google's proprietary system. Does anyone have any experience implementing this or any tips on where to start investigating a solution?