You need to add the following line to /etc/rmmount.conf:
share cdrom* -o ro
If the system isn't already acting as an NFS server, you'll need to run
# /etc/init.d/nfs.server start
In Solaris 2.6 and below, you will need to share something in
/etc/dfs/dfstab, otherwise mountd and nfsd won't be started.