Hi,
I don't know of such a util, but you could always write a script to do this.
E.g.: generate a list of clients for Windows and Unix/Linux with nsradmin
For Windows servers you could use the "sc \\clientname start/stop nsrexecd" to start/stop clients
For Unix/Linux servers I would use ssh/rsh to call the start/stop script in init.d.
I hope this helps.
BR,
Patrik