[Exim] $message_filename ?

Is the name of the temp file containing the current message
available so I can use it in a filter (.forward) file? E.g.,

    if "${run{bogofilter <$message_filename}{y}}" is y

Or is there a way to pass the message on standard input to $run?

If not, is this a reasonable enhancement suggestion..?

Thanks,

--
Bill Brelsford
k2di2@???