Splitting a delegated prefix on IPv6

Hi,
I have setup my router so that it obtains a delegated prefix under IPv6 and all works fine with advertisement and DHCPv6 so that I can register my DNS server on my clients. However, I would like to split my network so that the ‘guest’ section only gets the public DNS and the ‘corporate’ section only gets the private DNS. I use prefix delegation to get the pool and then use DHCPv6 to set the DNS server etc.

Can someone explain what I need to do - I get a /48 from my ISP so can easily split into two subnets that have different DNS settings?

Thanks
Mark