Split DNS

Hello,

I would like to use a Split DNS config for domain.com to have differnet
result on name resolution depending on the location (local or public)

So I have configured the public zone in a DNS provider, and installed a
BIND 9.2.2 on a local host. All local hosts are configured to use the
local DNS server.

It's work perfectly BUT, I have many public hosts that need to be
resolved identicaly whatever public or local name server is used.

With My actual install I have to synchronized manually these hosts
between my local DNS and the public one.

Is there a way to configue the domain.com zone in the local DNS server
to work like this :
- if the zone file contains the requested info, return it.
- if not forward the request to the public DNS server

I now how to do this if zone are distincts, but how to achieve that on a
single zone ?

Any suggestion greatly appreciated,

Carl.