How to remove users "only" on NIS database?

[Markos <markos@c2o.pro.br>]

Dear,

I have a small network with 6 machines running Debian Squeeze.

When installing the machines I created only the root account and a user
student1 in "all" machines on the network.

Then I installed a NIS Service on a machine (server), to centralize
logging of new users.

But now, I realized that if I shut down the server I can no longer login
as root, or student1, on the client machines.

How do I remove the accounts root and student1 "only" on the NIS
database on the server?

I want to login as root or student1 on the client machines with the
server off.

Is there any command like "delusernis" for Debian Squeeze?

Thanks for any help,
Markos