Interestingly - especially for those using an ASA without sufficient memory for later software versions - you can do this with ASA 8.0(3). It may have been an oversight or a "bug" with positive consequences in that version, because, it doesn't work in 8.0(5).
So I have a Cat4948 doing all the routing for my internal network. Now of course the 4948 doesn't support NAT, and since I'm on a domestic broadband service with only 1 public IPv4 address, I need something to do NAT, and that is an ASA, which of course is connected directly to my broadband.
The IPv6in4 tunnel remote endpoint (at the tunnel broker) is 18.104.22.168. The inside address of my end of the IPv6in4 tunnel is x.x.x.1/30.
The config is like this:
description Broadband Service
ip address dhcp setroute
ip address x.x.x.2 255.255.255.252
ipv6 address 2001:x:x:ff::2/64
ipv6 nd suppress-ra
object-group protocol IPV6inIP
access-list OUTSIDE-IN extended permit object-group IPV6inIP host 22.214.171.124 interface outside
access-list STATIC-IPV6TUNNEL extended permit object-group IPV6inIP host x.x.x.1 host 126.96.36.199
static (inside,outside) interface access-list STATIC-IPV6TUNNEL
access-group OUTSIDE-IN in interface outside
When I configure this, I get a warning about all traffic being translated to the interface address (IIRC) but it doesn't matter of course. I presume the warning applies only to protocol 41 traffic.