Server Side Mail Rules (aka Sieve) -- any way to do more complete rules?

Ok, so I got the Rules up and running just fine with 10.6.4.. They seem to work well but I'd like to use some of the Sieve capabilities to (among other things) look for certain mail headers and if present to something -- most of the time just stick the mail in a folder. The current implementation appears to mostly focus on the To:, From: and assorted recipients lists (e.g. bcc, cc) but completely skips this other area of the Sieve protocol.. I've got a complete sieve list from my old FreeBSD server (using Dovecot as well) and would like to be able to at least upload a new set of rules if not just edit them directly.. I guess Apple does not want people directly writing the rules but I've been doing that for the past 5 years and almost never had any issues. My only preference would be to be able to edit them without sitting in front of the server which of course is easy..

I suppose I could try to modify the existing rules editor to do what I want.. Anyone tried going down that path?