This code is in my emacs dot file now.
(setq org-html-preamble (lambda (an-arg) (or (cl-loop for idx from 0 upto 6 for fname = "org-html-preamble.html" then (apply #'file-name-concat (append (cl-loop repeat idx collect "..") (list (message "gbl/org/org-html-preamble_%d.html" idx)))) if (file-exists-p fname) return (org-file-contents fname)) "")))
(setq org-html-postamble (lambda (an-arg) (or (cl-loop for idx from 0 upto 6 for fname = "org-html-postamble.html" then (apply #'file-name-concat (append (cl-loop repeat idx collect "..") (list (message "gbl/org/org-html-postamble_%d.html" idx)))) if (file-exists-p fname) return (org-file-contents fname)) "")))