I've been trying to get this to work myself. As far as I've been able to understand, Swisscom gives us a /60. This should provide 16 /64 but actually only the first one is valid... and the Swisscom router takes it. It probably prevents DHCPv6 from getting to your router because the only available prefix (the /64) is already assigned on the Swisscom router.
As far as I've been able to figure out, our options currently are to turn the router into a transparent bridge/firewall or remove the Swisscom box out of the picture completely.