Adding "face" in conjunction with gnus-posting-styles

[Hadron]

I currently use the gnus-posting-styles attribute "x-face-file" which
takes an xface file as a parameter.

I wish to add a "face"

(http://gnus.org/manual/gnus_286.html)

I have this in my .gnus

(setq message-required-news-headers
           (nconc message-required-news-headers
                  (list '(Face . (lambda ()
                                   (gnus-face-from-file
           "~/.xfaces/face.jpeg"))))))

Could someone help me integrate it into gnus-posting-styles so it only
adds the face header if the group name contains "pattern".

thanks for any help.