(defun mytemp-file-handler (operation &rest args)
  "Bug test. Fall back to default handler."
  (let ((inhibit-file-name-handlers
         (cons 'mytemp-file-handler
               (and (eq inhibit-file-name-operation operation)
                    inhibit-file-name-handlers)))
        (inhibit-file-name-operation operation))
    (apply operation args)))
(put 'mytemp-file-handler 'operation '(insert-file-contents))

(defun mytemp-enable-handler ()
  (interactive)
  (add-to-list 'file-name-handler-alist
               (cons "\\.[a-z]+\\'" 'mytemp-file-handler) t))

(defun mytemp-disable-handler ()
  (interactive)
  (setq file-name-handler-alist
        (delete (cons "\\.[a-z]+\\'" 'mytemp-file-handler)
                file-name-handler-alist)))