"Any header" test - possible?

I am wondering how I could check for e.g. the existence of some text in
*any* header.  [With the text not being an email address so
that :address test is not what I really want].

RFC3028 (+bis) would imply that this is not possible. string-list that
is used in header-list has to have at least one string:

string-list = "[" string *("," string) "]" / string
                   ; if there is only a single string, the brackets
                   ; are optional

So saying

  header :contains [] "some text"

or 

  header :contains "some text"

,implying to match any header, is not valid.

So, is it possible to do what I want in Sieve?

-- 
Alexandros Vellis
avel(_at_)noc(_dot_)uoa(_dot_)gr