Dhcp config

[Kingston, Ken]

I have a system that has several thousand ip tv set-top boxes. I need to
configure dhcp to point a few (up to 100) to a test set of application
servers. They are all the same type of set-top box and are on the same
flat network. The only unique thing I have to key on is the mac address.
I have tried a combination of classes/subclasses but have had no luck
(still goes to the main pool and points to the production servers.
Anybody have a sample config that would do something like this.
 
Thanks