You can get round DNS issues by assigning your primary DNS server as your ISP's and your secondary as your internal DNS (LAN). If the client cannot access the LAN and therefore cannot resolve DNS using this server, then it will use the ISP DNS.

DNS isn't actually an issue - it's the allocation of IP addresses for the second subnet, which i want to keep isolated from the main network, but also provide WLAN connectivity.
Until Draytek add the facility, I think the easiest way around this is add an old cable router on a VLAN, this will do what i need, bt providing the isolation and serving it's own DHCP for the second subnet..

Yes! I need this too!

Please, please add this.

I second this also, but does sound like another request for better dhcp pool control per Port & VLAN.

http://www.forum.draytek.co.uk/viewtopic.php?p=61046#61046

&

http://www.forum.draytek.co.uk/viewtopic.php?t=12394

(There seems a running theme for this feature, in various forms - I hope it comes soon.)

Another request in the same vein (if another will make any difference !)
I have DHCP set up on a 2008 box, and I want to segregate my non-domain clients from my domain ones. So, I specify isolation from the LAN in the mac filtering for the non-domain clients, but without access to my 2008 server, they don't get a lease (as I have to disable DHCP on the 2820Vn otherwise my domain clients don't get my DCs DNS, so don't do group policy or roaming profiles). I tried the 2nd DHCP server configuration, but that was no help. There should be a way to prevent access to the LAN, but get a DHCP lease.