[Exim] Auto freeze

I wonder, is it possible to automatically freeze a message in Exim?
I know there's the -Mf option, and the auto_thaw option, so how about the
converse, and be able to specify auto_freeze in a transport?

           Norman McBride                      "Blessed is the norm."
           http://www.alces.net/~norm/                   John Wyndham