Basically I want to be able to replace this radvd configuration snippet:

interface br-lan
{
        AdvSendAdvert on;
        AdvManagedFlag off;
        AdvOtherConfigFlag off;

        route fc00::/8
        {
                AdvRoutePreference medium;
        };
};

It statically advertises a route for the fc00::/8 address space on all LAN interfaces, nothing else; no assigning addresses, no extra subnet routes, just handing out that single route. This this possible with odhcpd right now? Is it hard to implement?