split DNS for clients through a proxy

[Humphrey]

I need to know if there is a way to create a split forwarding DNS server
with BIND 9 such that two groups of client machines are being serviced
indirectly by two different external DNS servers. The purpose for this
is to use the adult content filtering functionality of OpenDNS for
machines used by children and another non-filtering DNS for machines
used by adults. Yes, I do understand this is easily done using BIND 9
views, but that depends on knowing the client machine's IP address. So
here comes the wrinkle... All client machines are configured such that
their web browsers go through a Privoxy proxy which resides on the same
machine as the forwarding DNS service. The result of this is that client
machines do not actually make the DNS queries - Privoxy does this for
them, which means the forwarding DNS server only ever sees the queries
as coming from its own IP address. The question is whether anyone knows
of a way of achieving the split-DNS effect in this scenario.

H.