I am administering a very small solaris 2.6 network with 4 boxes total. Is it possible to use scp or similar to replace NIS for synchronizing users, groups, hosts, etc?

This network is only a small part of my job and I don't want to spend too much time on it, and I am worried the setup and maintenence of NIS will not pay off. I need it to behave like a proper multi-user system, when a user logs into any machine, the users, passwords, hosts, etc. are always the same.

Is there an easy way to do this with scp? Right now I copy /etc/passwd from one box to another with scp, but sometimes I make mistakes or forget a step, and scp inside of shell scripts don't seem to works so well since they require password authentication. Any recommendations would be welcome.