There is a button in the dashboard. A script of theirs will alter your MAC address and reboot your machine. When it comes back up, IPv6 is working like a champ.
I just did mine; I got a new IPv6 address and the same IPv4 address.
Well, there went my excuse. I tried to set up a tunnel the other day and couldn't get it to work, but this worked like a champ. I can proudly say my client now owns two of the few IPv6-enabled porn sites on the planet.
CloudFlare handled the DNS like a champ (although I did have to disable and re-enable acceleration for one of the domains to get it to work).