I think that's indeed the correct place. I'd add some comments though, something like:

/**
 * This is essentially the plugin version of get_enum_element in core/helper_api.
 * Given a plugin enum string and num, return the appropriate string for the
 * specified user/project
 * @param string $p_enum_name
 * @param int $p_val
 * @param int|null $p_user user id, defaults to null (all users)
 * @param int|null $p_project project id, defaults to null (all projects)
 * @return string
 */