DHCPv6-PD -> Lack of route injection in RFC

I am running into venders that do not support injection of a delegated route when operating as a DHCPv6 relay (or server for that matter). Brocade supports this, but I am not finding this as part of any of the RFC's. This is to deliver home ISP service, so it is very important or return packets won't go to the client unless the route is manually added as a routing protocol is not an option. There should be a MUST activity for this somewhere. Anyone know what gives?