Dhcpv6-server handing out addresses from delegated prefix?

I am running a fairly resent build of 1.3 and have managed to get a delegated /60 prefix from an upstream router and hand out addresses via slaac to lan clients based on the instructions in soucys super guide at http://soucy.org/vyos/DHCPv6-PD_on_VyOS.pdf

Now I am looking to supplement the setup to also be able to hand out statefull addresses using dhcpv6.

The dhcpdv6 example in DHCP Server — VyOS 1.3.x (equuleus) documentation show an example with a static prefix but not how to use configure a “dynamic” delegated prefix.

I have tried replacing the static prefix with ::/64 the same way as the route-advertisment config for slaac

set service router-advert interface eth1 prefix ::/64

but that does not seem to work.

Has anyone managed to get this working ?