[RndTbl] procmail global rule?

I'd like to have a global procmail rule that applies to all users on a system. I tried putting it in /etc/procmailrc, but that doesn't seem to execute at all. Each user on the system has their own ~/.procmailrc. I'd like to have the global one always apply, and the user's own apply also (after) the global rule. Anyone know how to do this? Thanks!