Both Microsoft and our Microsoft partners failed to make this work. Infoblox shows a solution for a paid software alternative. Our go to solution for customers now is to use SLAAC for phones and have them get their options from the a local Cisco router. Using M=0, A=1, O=1 will disable DHCP, use SLAAC to generate an address, but then will go do DHCP to get their options which we point the IPv6 relay to a Cisco router and have it hand out the TFTP, DNS, and domain name. This uses the Cisco router, but keeps the load light. Since not handing out addresses you don't need a scope for each subnet, just one set of global configs for all. Not using DHCP is a shock to network and security teams, but when you drill down to why they need it, there are better ways to handle their needs and tracking abilities.
