Flex Objects and directory

Is it possible to use flex objects with variable directories? Usually the directory has to be specified in the flex-blueprint under

      class: 'Grav\Framework\Flex\Storage\SimpleStorage'
          class: 'Grav\Framework\File\Formatter\JsonFormatter'
        folder: user-data://flex-objects/guestbook.json

Would it be possible to define the folder variably?

Use case would be a guestbook plugin with multiple storage directories that can be specified in the frontmatter of a md page file. This way each page could have its own storage directory.