limit strike-through to the width of the string in gnus-summary-mode-line-format

[Julien Cubizolles]

I'm using the strike-through face spec pour the gnus-summary-cancelled
face. The striking line runs all the way to the last column of the
buffer but I'd like it to not strike the spaces used for padding.

With


--8<---------------cut here---------------start------------->8---
(copy-face 'gnus-summary-normal-unread 'gnus-face-5)
(set-face-attribute 'gnus-face-5 nil :strike-through nil)
(setq gnus-face-5 'gnus-face-5)
(set-face-attribute 'gnus-summary-cancelled nil :strike-through t)
(setq gnus-summary-line-format "%5{%U%R%z%I%(%[%4L: %-23,23f%]%)%} %s\n")
--8<---------------cut here---------------end--------------->8---

gnus-summary-delete-article will strike through the subject field and
also through the spaces following it. I'd like it to stop at the end of
the %s field. I've played around with tabs %=, cutting and maxing,
padding but there always something wrong, mostly because I don't know
the length of the string of spaces that will be added after the %s
subject.

Is there a way to get to specify a face, with %number{%s%} but only for
the length of the %s string inserted ?

-- 
Julien Cubizolles