Serve DHCPv6 while using SLAAC

[junicast]

When I have choosen SLAAC for my downstream interface while IPv4 being deactivated.
I cannot choose to run a DHCPv6 server on that interface because of my choice.
Link Local addresses do suffice AFAIK even for routing global traffic, isn't it?

The funny thing is that my upstream device, which happens to be my own pfSense, doesn't respond to DHCPv6 solicitations, which I think is an unhandled bug in pfSense. So I cannot choose "Track Interface" as an option because DHCPv6 is simply broken.
I too cannot choose SLAAC which is actually my preferred method since I would want to be able to run DHCPv6 together with IPv6 Prefix Delegation or RA on the downstream device.