Enabled SSL inspection but now Chromebooks can't connect

[jpl63]

We have a Fortigate 100D runnning v6.0.7. We've recently activated SSL inspection and web filtering, which required a certificate installed on every computer. The problem is the Chromebooks--they are not connecting at all. These are not on a domain, so they don't get the certificate via GPO. I can't get the cert to install from the Google admin console, but if I  install the cert manually, it works fine. Of course, the cert only installs to the user profile on the Chromebook, so any other user has to get it installed separately. That could result in hundreds of manual installs. I can't figure out how to get the cert to the Chromebooks through Google. I've tried to push it from an open guest network, but no joy. Any ideas?