[Exim] Use of wildcards

I use a shared server which runs Exim 3.16 (out of date but out of my
hands).

I use the .forward file as a spam filter for my incoming mail but recently
more spam has been getting through due to the use of various substitute
characters for "i".

Is there a way I can use wildcards when I'm checking the headers, as in:

  if
    $header_subject: contains "str?ng conta?n?ng w?ldcards"
  then
    save $home/.mail/junkmail
    finish

where the question mark is a wildcard character?

thanks,

Pete Horn