Limit org-caldav to org-id-files only in specific directories?

[emacsomancer]

I have a lot of org-id-files, but I only want org-caldav to look at/deal with org-ids which are in files in particular directories. I currently have just brute force done this (after also setting org-caldav-calendars to the org files I want it to deal with)

  (setq org-id-files-temp nil)
  (defun bms/org-caldav-remove-org-id ()
    (setq org-id-files-temp org-id-files)
    (setq org-id-files nil))
  (defun bms/org-caldav-restore-org-id ()
    (when (not (equal org-id-files-temp nil))
      (setq org-id-files org-id-files-temp)))
  (advice-add 'org-caldav-sync :before #'bms/org-caldav-remove-org-id)
  (advice-add 'org-caldav-sync :after #'bms/org-caldav-restore-org-id))

But I wonder if there is a better way?