Add a public ''subscribed-to'' calendar to free/busy

Add a public ''subscribed-to'' calendar to free/busy

I subscribed to a public calendar which belongs to me (created under Google Agenda). It is shown under "Other Calendars" rather than under "My Calendars". I'd like to use this calendar and include it in my "free/busy" information so that the rest of the organization know when I am unavailable due to event scheduled in my Google Account.