However, there are NAT boxes which have a feature to enable an IPv6 over IPv4 tunnel over NAT. If your NAT box has such feature, you can use the option of the dtcp to support NAT traversal.
If your NAT box has a feature that
you can configure your NAT box to forward the packet which protocol number is 41, to your tunnel box inside of your NAT, or,perhaps you'll win.
you can configure your NAT box to forward all packets to your NAT box, to your tunnel box inside of your NAT box.
Try -n option of dtcpc or dtcpclient with above setting into your NAT box.
The dtcps has an option to serve DTCP from inside of your NAT, too. But, you need to specify an IPv4 global address of outside of your NAT box by -g option.