I think that RADV, which adds the possibility for stateless configuration, is an important difference between IPv4 and IPv6.
Of course, router advertisements and router solicitations will not traverse routers, so a tunnel would be needed...
The user would have to set up a tunnel (either IPv6 in IPv6 or IPv6 in IPv4) with a dedicated host at he.net. For the test, HE would send a router solicitation through the tunnel and wait for a router advertisement (perhaps using the 2001:DB8::/32 prefix). The use of RDNSS might also be required.
What do you think of this idea?