[Samba] Samba4 Internal DNS and local forwarding

[John]

I have a working Samba configuration with an internal DNS for a small
office. Elsewhere on the network is a router providing DNS and DHCP
services to the network (consider it a black box without administrative
access). Samba is configured to use that as its DNS forwarder.

My problem is that the Samba DNS knows nothing about any DNS entries
created on the router, either static or from the DHCP server, and
doesn't forward requests for its own local domain that it cannot resolve
itself (Of course, forwarding for non-local domains works as it should).

The effect can be demonstrated:

    $ ping a_host
    ping: unknown host a_host

Is it possible to configure the internal DNS so that it also forwards
local requests that it's unable to resolve itself ?

I have read this
(https://lists.samba.org/archive/samba-technical/2013-December/096572.html)
that says it can't. I've also seen a similar question on SE
(http://serverfault.com/questions/670979 ) that doesn't provide an answer.

If it's true that Samba's DNS can't forward local requests then how
should this scenario be catered for?

Guidance appreciated.
John