Edit /etc/fstab, comment out your /var entry, reboot.  Might want to
  edit /etc/rc.conf, set things that want /var to contain stuff
  (named, sendmail, etc) to not start.

when doing this, make sure not to mess up /var/chroot/sshd.  I just
had a machine fail to start ssh since /var/chroot/sshd was owned by me
instead of root.  So perhaps rsync what you can from /var first to
/var.new and put something in rc to mv it to /var on startup.

-- 
        Greg Troxel <gdt@ir.bbn.com>