I have the following declarations in my ~/.gnus file:

(setq gnus-buttonized-mime-types '("multipart/encrypted" "multipart/signed" "multipart/related" "multipart/alternative"))

(custom-set-variables
 ;; Avoid text/html parts if possible (w3-mode is slow).  Also avoid
 ;; text/enriched, since it's often more difficult to read.
 '(mm-discouraged-alternatives '("text/html" "text/enriched"))

 ;; Buttonize text/html rather than display it automatically.  It's frequently
 ;; spam and I don't want to incur the wait to have it render.
 '(mm-automatic-display (remove "text/html" mm-automatic-display))
)

As a consequence, when a message arrives from someone that uses a
(stupid, useless) HTML mail reader, I see the text/plain alternative
by default, but I get a button so that I can tell that there is an
HTML alternative. (This helps for those rare cases where their client
botches the text/plain alternative).

However, I also get the occasional message where the text and HTML
parts aren't sent as alternatives, but rather as multipart/related. In
this case, I get the buttons, but the HTML is displayed by default.

How can I configure things so that the text/plain related part is
displayed by default in this case?

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | The present moment is a powerful
http://nwalsh.com/            | goddess.-- Goethe