qmail/vpopmail/procmailrc

I have a qmail/vpopmail setup on a machine and am wondering if there are 
filtering options for vpopmail users? (like procmailrc).

As the .procmailrc is not something they can edit because they don't 
technically have a user on the machine, what should I suggest to those 
who ask for procmailrc when I'm not sure how that would work so they 
could edit it (through squirrelmail plugin or through a web based editor 
of some sort). Does the user have some way to edit this that I might not 
be aware of? If a file exists in  
/home/vpopmail/domains/domainname.com/robby do I have access to edit 
robby/.procmailrc if I authenticate through the IMAP server?

Just curious as to what options I have for handling this, if I have 
access to their dir from IMAP auth, I could build a simple webpage they 
login to and manage a procmailrc file (or any other files in that 
directory for that matter).

thanks in advance,

-Robby