How to use each machines's HD as a backup with Lion Server accounts?

Hi,

I am the administrator of a network for a small business.

We have 6 machines (iMac running OSX Lion) and one Mac Mini running OSX Lion Server.

Every user is logging on their machines with their network account, which means that they (by default) save all their documents on the Mac Mini server.

The good side of this is that:

a) Any user can log in from any machine

b) Every document that the user has is backed-up at regular time intervals thanks to Time Machine.

Although the networks access tends to slow down the machine (especially with big Excel spreadsheets), and each iMac has massive hard drives that are all 95% empty.

Is there a way to easily setup an appropriate policy so that I can leverage the big size of each machine's hard drive, and reduce network access?

(i.e. each user loads all the configuration from the network at login, then works on his/her local drive until he/she logs out, and a full back-up from the local drive to the distant folder is made once a day / once a week???)

Thanks,