Checking another DNS server if first server returns no records

Hi,

I have a short question about local-zone options.

Is there a way todo the same thing as the option "transparent" but in reverse order?
First checking external DNS and if not exist check local-data or better check another DNS Server?

The problem which I try to solve is that we have an external and an internal DNS server returning diffrent IPs for the same record (public and local IPs). In some cases a records doesn't have an external IP and the DNS Server responses with no information. In this case unbound should check another DNS (the internal) for a DNS record.

thx

Harald