You will need to enable the #+BIND keyword by adding this to your init file
and restarting emacs
(setq org-export-allow-org-bind-keywords t)
You can also customize this variable (which allows you to skip the restart).
Then you can assign to export-related variables even if there is no option for them (as in this case), by adding the following header to your ...
Try this function:
(defun my/org-export-headline (&optional backend async subtreep visible-only body-only ext-plist)
"Export the current Org headline using BACKEND.
The available backends are the ones of `org-export-backends' and
When optional argument SUBTREEP is non-nil, transcode the
sub-tree at point, extracting information from the ...