[O] Binding org-html-head to a function?

[Sébastien Brisard]

Hello,
my blog (sbrisard.github.io) is entirely written with org-mode. Org-mode 
offers everything I need, except for one minor detail. It is very 
difficult to include the same CSS file in the html-head of several files 
located at various levels of the directory hierarchy.
I do not really like this trick 
http://orgmode.org/worg/org-tutorials/org-publish-html-tutorial.html#sec-6. 
For the time being, I configured several projects (one for each level), 
see https://github.com/sbrisard/blog/blob/master/sb-blog.el. But I am 
not happy with this solution either.
I think that it would be great if org-html-head and org-html-head-extra 
behaved as org-html-preamble and org-html-postamble, which can be set to 
either a string, or a function. This offers great flexibility for the 
configuration of the pre/postamble (I use it to conditionnaly include 
DISQUS comments in the postamble).
Would it be possible to mimick the same behavior with org-html-head and 
org-html-head-extra? Or would this be too much work?

Thanks for your thoughts,
Sébastien