Wiki – how to extend to full width in twenty fourteen theme

I posted this question before at and had a reply giving me some new code for Wiki. Unfortunately it did not work, and I have not been able to get any further updates.

I want to be able to use the full width page for Wiki. I am using the new Twenty Fourteen theme, and in order to select Full Width for regular pages and posts it is a simple matter of selecting the full width template. This option is not available with Wiki. I have also been able to achieve this with forums by using a short code on a new page – an option also not available for Wikis. This is a critical part of my site, so any help would be much appreciated. You can see the current set up here

I am beginning to see that this is a frequent requirement from users of the Twenty Fourteen theme. I see that the Extended plugin (a great piece of work) allows full width to be selected as the default for posts and archives, but not for pages and not for Wikis.