IPv6 from WAN to LAN throughpass methods

[Axent1987]

Hello. I have a router with LAN and WAN ports.
I am using WAN with ipv6. It works well on router side. I can ping and reach ip6's resources in Internet. But I cannot do this from LAN (no IPv6). So routing diagram inside the router should looks:
LAN<--------->WAN
I figured out that the problem is related missing delegated prefix from ISP router. In Wireshark DHCPv6 packet shows in Advertise message 'NoPrevixAvail'. For some reason my router doesn't insert IP_PD-options in Solicit request and the ISP searches for 64 length prefixes by default. Or maybe something else is wrong that causes the answer with no prefixes.

But if I set the static ipv6 prefix (option ip6prefix) with gateway and source in settings I can get IPv6 working on LAN.
The common problem that not each ISP can provides the Prefix. And it force me to set the static Prefix and all works fine.
Question. What another method can be used to get throughpass of IPv6 between WAN and LAN except the Prefix Delegation?
Thanks.

[mk24]

Try different reqprefix sizes on wan. Common values are 56, 60, 48, and 64. Some ISPs do not send a prefix unless your router requests exactly the length they expect.

If you know that your ISP is not going to change your prefix it is ok to configure it statically.

[Axent1987]

The static ipv6 prefix is not the problem.
The problem is that the router is ... roaming. It can be connected for different ISP's per month and I am looking for more flexible solution in cases where 'NoPrevixAvail'. I even wrote little sh-script to check inserted cable event and parsing input connection to form needed static ip6prefix. Then using uci commands the script changes settings and restart network.
But I think you ll agree that it is ugly workaround.