I just did a little research on cron and found this: it looks like all
crontab does is check your syntax so you aren't installing bad crontabs.
>From what I can tell when cron loads it looks in /var/spool/cron for
crontabs of users in /etc/passwd. Then it also looks for /etc/crontab.
It will look for mod times on it's spool directory and /etc/crontab
every minute, and if one has been modified, then it will reload all
crontabs. So I tried updating my crontab in /var/spool/cron, as root,
and sure enough it worked. So it looks like all we will have to do is
edit the /var/spool/cron directly (once we figure out the permissions
problem), and it should work.