If you have a IP Adress like 2001:41d0:0601:1100:0000:0000:0000:091c and your gateway is 2001:41d0:0601:1100:0000:0000:0000:0001 this 3 commands will give you the whole IPv6 World:

ip -6 addr add 2001:41d0:0601:1100:0000:0000:0000:091c/128 dev eth0
ip -6 route add 2001:41d0:0601:1100:0000:0000:0000:0001 dev eth0
ip -6 route add default via 2001:41d0:0601:1100:0000:0000:0000:0001 dev eth0