I can't reproduce this behavior from the UK. In any case, DNSmasq (the DNS cache daemon that is part of OpenWRT) has an option to filter bogus NXDOMAIN response

I can't reproduce this behavior from the UK. In any case, DNSmasq (the DNS cache daemon that is part of OpenWRT) has an option to filter bogus NXDOMAIN responses if you can get a list of the IPs. Alternatively, run your own recursive resolver and cache, it's worth it.