(let ((counter 0))
  (defun ox-mrkup-filter-src-block (text back-end info)
    (let* ((url (save-nth-src-block counter (plist-get info :parse-tree)))
          (output   (format "%s 

<a href=\"%s\">Open the code</a> 

" text url)))
      (setq counter (+ counter 1))
      output))

  (let ((org-export-filter-src-block-functions '(ox-mrkup-filter-src-block))
        (async nil)
        (subtreep nil)
        (visible-only nil)
        (body-only t)
        (ext-plist '()))
    (org-html-export-as-html async subtreep visible-only body-only ext-plist))

    ; now get the output into the org output
    (switch-to-buffer "*Org HTML Export*")
    (buffer-string))