One way to get IPv6 /64 bridged to your LAN:
brctl addbr br0
brctl addif br0 eth0
brctl addif br0 eth1
ebtables -t broute -A BROUTING -p ! ipv6 -j DROP
ifconfig br0 up
Opened up: create software bridge from your WAN -interface to LAN -interface, but allow only IPv6 to fly over it. In my setup IPv4 is natted.