NIS user audit?

Hi

I'm happily running NIS on Debian woody to authenticate users running
diskless workstations, but I'd love to be able to have a log of which user
logged into what workstation and, most importantly, when

Is this possible? I've considered running ruserd on each workstation and
polling it every minute, but this seems a little inelegant.

Any ideas would be very welcome

Cheers,
Gavin.