caching only Bind w/override of some names

[fropnorlm]

I have bind setup as caching-only (works correctly),
but I want to do the following - override 2 different
A records for an external domain:
smtp1.attglobal.net / smtp2.attglobal.net - and point
them to my internal sendmail server. Why? Roadwarriors.
When they are out in the field - they will get the correct IP's
returned by the real attglobal.com servers, but in the office
I want to return the IP of my mailserver. This will make it a
seamless process for them - just come in the office - plug
in to the network - and presto - they can send mail no problem.
I understand that I can add a zone for attglobal.net to Bind,
but that would mean that I would have to manually update that zone
as it changed - no fun.

Is there any way to do this? If it matters - Bind is running chroot on
OpenBSD.

Thanks.