backing up shadow files with rsync?

[Robert Moskowitz]

How would you back up /etc/passwd and its shadow file (and the same for 
/etc/groups) using rsync?

In my case, I have a USB drive to back stuff up to.  I already have a 
cron job, backing up /home

And then, for my documentation, how would I restore the shadow files?

This is to provide for disaster recovery (which I am in the middle of 
right now without proper backups...).