A question about nsupdate

[Who wants to Know?]

I am running Bind 8.1.2 with approx. 750 zone files.

I want to be able to dynamically add CNAME records using nsupdate. 

It works, but is very slow.

I run nsupdate, with an update add command and I notice that a '.ixfr' file
and a '.log' is created for the domain being updated but the .hosts file 
doesn't change right away. After a period of time (about 30 minutes?) the 
.log file disappears and the .hosts file is updated with the new RR.

Does anyone know  if there's a way of having Bind update the .hosts
file immediately.

Any help would be appreciated.

Thanks.  Martin Downes.