cron mails threading

[Elliot S]

I finally got around to getting gnus set up to read my server's
emails. It looks like every e-mail with the same subject is getting
threaded in to one conversation:

O. [  27: Cron Daemon            ] Cron <updates@...>    aptitude
update
R.     <  27: Cron Daemon            >
...
O. [   8: Cron Daemon            ] Cron <clamav@...>  freshclam
O.     <   4: Cron Daemon            >
...

So, I get a small number of long threads. I somewhat remember there
being a way to set a custom threading function (gnus psychosis is a
warm, fuzzy, forgetful feeling). It'd be nice to prefix that with an
exception for cron (say, don't thread these mails) then hand
everything off to the defaults. Any thoughts?