greylisting before tmda confirm

I'd like to greylist messages otherwise headed for .tmda/pending.

By the time my mail gets to tmda it has already been run through
spam-assassin and my own maildrop script. However, I still need
to decrease the time I spend checking my .tmda/pending messages.

I would like to add a greylisting script in my .qmail files after
maildrop and before tmda. I have a good idea how to make this work
in my specific system of maildrop script + tmda filters.

What are some decent greylist solutions that run well this way?
I'd prefer something easily installed on a shared host server
and would love to see something that uses line-delimited text
files to read in TO addresses on which to apply greylisting.
(ie. The same file I use in: to-file -autocdb ~/tgray confirm)

-- 
 kai