This is a problem that i'm starting to see more often; same subnets in use at home-users and the corporate LAN.
I personally have found no solution for this problem, for as far as i know is this only possible with a LAN-2-LAN tunnel. See the following page for the solution for the same problem with a LAN-2-LAN tunnel:
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...